Health Library

The H1N1 virus (swine flu) is a new virus strain that has caused a worldwide pandemic in humans from June 2009 to August 2010. The Centers for Disease Control and Prevention now call the virus 2009 H1N1.

H2 receptor antagonists are medicines that help decrease stomach acid. H2 receptor antagonist occurs when someone accidentally or intentionally takes more than the normal or recommended amount of this medication. This is for information only and not for use in the treatment or management of an ...

Hair poisoning occurs when someone swallows this substance. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison Control Center at ...

Hair dye poisoning occurs when someone swallows dye or tint used to color hair. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison ...

Partial or complete loss of hair is called alopecia.

Hair spray poisoning occurs when someone breathes in (inhales) hair spray. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison Control ...

Hair straightener poisoning occurs when someone swallows chemicals used to straighten hair. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National ...

Hair tonic is a product used to style the hair. Hair tonic poisoning occurs when someone swallows this substance. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as ...

A hair transplant is a surgical procedure to improve baldness.

Hairy cell leukemia (HCL) is an unusual cancer of the blood. It affects B cells, a type of white blood cell (lymphocyte).

Hallervorden-Spatz disease is a movement disorder that is passed down through families (inherited).

Hallucinations involve sensing things while awake that appear to be real, but instead have been created by the mind.

The Ham test is done to diagnose (PNH). The test checks whether red blood cells become more fragile when they are placed in mild acid.

Hammer toe is a deformity of the toe, in which the end of the toe is bent downward.

Hand lotion poisoning occurs when someone swallows hand lotion or hand cream. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison Control ...

Spasms are contractions of the muscles of the hands, thumbs, feet, or toes. Spasms are usually brief, but they can be severe and painful. See also:

A hand is a medical image of one or both hands.

Hand-foot-mouth disease is a relatively common infection viral infection that usually begins in the throat. A similar infection is .

Hantavirus is a life-threatning disease spread to humans by rodents.

Haptoglobin is a protein produced by the liver. It connects to a certain type of in the blood. A blood test can tell how much haptoglobin you have in your blood.

Hartnup disorder is an inherited condition that involves the transport of certain (for example, and histidine) in the small intestine and kidneys.

HbA1c is a test that measures the amount of glycated in your blood. Your doctor may order this test if you have diabetes.

A qualitative HCG blood test checks to see if there is a hormone called in your blood. HCG is a hormone normally produced during pregnancy. See also: (reveals specific level of HCG in your blood)

A quantitative human chorionic gonadotropin (HCG) test measures the specific level of HCG in the blood. HCG is a hormone produced during pregnancy. See also:

This type of human chorionic gonadotropin (HCG) test measures the specific level of HCG in the urine. HCG is a hormone produced during pregnancy. See also:

HDL stands for high-density lipoprotein. It’s also sometimes called “good” cholesterol. Lipoproteins are made of fat and protein. They carry cholesterol, triglycerides, and other fats, called lipids, in the blood from other parts of your body to your liver. This article discusses ...

Head and face reconstruction is surgery to repair or reshape deformities of the head and face (craniofacial). See also:

Head circumference is a measurement of a child’s head around its largest area — it measures the distance from above the eyebrows and ears and around the back of the head.

A head injury is any trauma that leads to injury of the scalp, skull, or brain. The injuries can range from a minor bump on the skull to serious brain injury. Head injury is classified as either closed or open (penetrating). A closed head injury means you received a hard blow to the head from ...

Head lice are tiny insects that live on the scalp. They can be spread by close contact with other people. These lice only live in hair and occasionally eyebrows and eyelashes. See also:

A magnetic resonance imaging (MRI) scan of the head is a method to create detailed pictures of the brain and surrounding nerve tissues. Unlike and computed tomographic () scans, which use radiation, MRI uses powerful magnets and radio waves. Signals from the magnetic field bounce off your body ...

A headache is pain or discomfort in the head, scalp, or neck. Serious causes of headaches are very rare. Most people with headaches can feel much better by making lifestyle changes, learning ways to relax, and sometimes by taking medications. See also:

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

All adults should visit their health care provider from time to time, even if they are healthy. The purpose of these visits is to: Screen for diseases Assess risk of future medical problems Encourage a healthy lifestyle Update vaccinations Maintain a relationship with a doctor in case of an illness

Hearing loss is the total or partial inability to hear sound in one or both ears. See also:

Hearing loss is the total or partial inability to hear sound in one or both ears. This article focuses on hearing loss in infants.

The body’s cardiovascular, or circulatory, system is made of the heart, blood, and blood vessels (arteries and veins). Heart and vascular services refers to the branch of medicine that focuses on the cardiovascular system.

A heart attack is when blood vessels that supply blood to the heart are blocked, preventing enough oxygen from getting to the heart. The heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction.

A is a medical emergency. The average person waits 3 hours before seeking help for symptoms of a heart attack. Many heart attack victims die before they reach a hospital. The sooner someone gets to the emergency room, the better the chance of survival. Prompt medical treatment also reduces the ...

Heart bypass surgery creates a new route, called a bypass, for blood and oxygen to reach your heart. See also:

Heart bypass surgery creates a new route, called a bypass, for blood and oxygen to reach your heart. Minimally invasive coronary (heart) artery bypass can be done without stopping the heart and putting a patient on a heart-lung machine. See also:

A computed tomography (CT) scan of the heart is an imaging method that uses x-rays to create detailed pictures of the heart and its blood vessels.

Heart disease is any disorder that affects the heart’s ability to function normally. Various forms of heart disease include: - alcoholic (myocardial infarction)

A healthy diet is a major factor in reducing your risk of heart disease.

Mention the term "" and most people imagine a pudgy, middle-aged man drenched in sweat and clutching his chest. Few people seem to consider cardiovascular disease (CVD) as a woman’s disease. But according to the American Heart Association, cardiovascular disease is the leading ...

Heart failure, also called congestive heart failure, is a condition in which the heart can no longer pump enough blood to the rest of the body.

Heart (MRI) is a imaging method that uses powerful magnets and radio waves to create pictures of the heart. It does not use radiation (x-rays). The test may be done as part of a . Unlike and computed tomographic () scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI ...

Murmurs are blowing, whooshing, or rasping sounds heard during a heartbeat. The sound is caused by turbulent blood flow through the heart valves or near the heart.

A pacemaker is a small, battery-operated device that senses when your heart is beating . It sends a signal to your heart that makes your heart beat at the correct pace.

Palpitations are heartbeat sensations that feel like your heart is pounding or racing. You may simply have an unpleasant awareness of your own heartbeat, or may feel skipped or stopped beats. The heart’s rhythm may be normal or abnormal. Palpitations can be felt in your chest, throat, or ...

A heart positron emission tomography (PET) scan is an imaging test that uses a radioactive substance (called a tracer) to look for disease or poor blood flow in the heart. Magnetic resonance imaging () and computed tomography () scans reveal the structure of the heart. A PET scan can tell your ...

Heart transplantation is surgery to remove a damaged or diseased heart and replace it with a healthy donor heart.

Heart valve surgery is used to repair or replace diseased heart valves. Blood that flows between different chambers of your heart must flow through a heart valve. Blood that flows out of your heart into large arteries must flow through a heart valve. These valves open up enough so that blood can ...

A heart–respiratory monitor can measure a baby’s or child’s: Breathing rate Heart beat Oxygen level Caregivers can use these measurements to determine how the baby or child is doing, and help make decisions regarding treatments and medicines. The monitor often uses stick-on electrodes, ...

Heartburn is a painful burning sensation in the esophagus, just below or behind the breastbone. The pain often rises in your chest and may radiate to your neck or throat.

Heat emergencies fall into three categories of increasing severity: heat cramps, heat exhaustion, and heatstroke.

Heat intolerance is the inability to be comfortable when external temperatures rise.

The Heimlich maneuver is an emergency technique for preventing suffocation when a person’s airway (windpipe) becomes blocked by a piece of food or other object. See also:

Helicobacter pylori (H. pylori) is the bacteria responsible for most and many cases of stomach inflammation (chronic gastritis). The bacteria can weaken the protective coating of the stomach, allowing digestive juices to irritate the sensitive stomach lining.

HELLP syndrome is a group of symptoms that occur in pregnant women who have: H — (the breakdown of red blood cells) EL — elevated liver enzymes LP — low

A hemangioma is an abnormal buildup of blood vessels in the skin or internal organs.

Hematocrit is a blood test that measures the percentage of the volume of whole blood that is made up of red blood cells. This measurement depends on and the size of red blood cells. The hematocrit is almost always ordered as part of a .

Hemochromatosis is a disorder that results in too much iron being absorbed from the gastrointestinal tract.

Hemoglobin is a protein in red blood cells that carries oxygen. A blood test can tell how much hemoglobin you have in your blood. See also:

Hemoglobin C disease is a blood disorder passed down through families. It leads to a type of anemia, which occurs when red blood cells break down earlier than normal.

Hemoglobin derivatives are altered forms of , a protein in red blood cells that moves oxygen and carbon dioxide between the lungs and body tissues. This article discusses the test used to detect and measure the amount of hemoglobin derivatives in your blood.

Hemoglobin electrophoresis is a test that measures the different types of the oxygen-carrying protein () in the blood.

Hemoglobinopathy is a group of disorders passed down through families (inherited) in which there is abnormal production or structure of the molecule. Such disorders include , hemoglobin S-C disease, , and various types of .

Hemoglobin is a molecule attached to red blood cells that helps move oxygen and carbon dioxide through the body. Red blood cells have an average life span of 120 days. After this time, they are broken down into parts that can make a new red blood cell. This typically takes place in the spleen, ...

Hemolysis is the breakdown of red blood cells. See also:

Hemolytic is a condition in which there are not enough red blood cells in the blood, due to the premature destruction of red blood cells. There are a number of specific types of hemolytic anemia, which are described individually.

caused by chemicals and toxins is a lack of enough red blood cells due to the destruction of red blood cells triggered by exposure to certain chemicals or toxins.

Hemolytic crisis occurs from the rapid destruction of large numbers of red blood cells (). The destruction occurs much faster than the body can produce new red blood cells.

Hemolytic-uremic syndrome (HUS) is a disorder that usually occurs when an infection in the digestive system produces toxic substances that destroy red blood cells, causing kidney injury.

Hemophilia refers to a group of bleeding disorders in which it takes a long time for the blood to clot. Related topics:

Hemophilia A is a hereditary caused by a lack of blood clotting factor VIII. Without enough factor VIII, the blood cannot clot properly to stop bleeding.

Hemophilia B is a hereditary bleeding disorder caused by a lack of blood clotting factor IX. Without enough factor IX, the blood cannot clot properly to control bleeding. See also:

Hemorrhage is the medical term for bleeding, usually excessive bleeding. Hemorrhagic diseases are caused by, or result in, bleeding (hemorrhaging). See also: (hemorrhagic thrombocythemia)

Hemorrhagic disease of the newborn is a bleeding disorder that usually develops shortly after a baby is born.

Hemorrhoid surgery is the removal of swollen veins around the anus (). Hemorrhoids can be inside (internal) or outside of (external) the skin around the rectum.

Hemorrhoids are painful, swollen veins in the lower portion of the rectum or anus.

Hemothorax is a collection of blood in the space between the chest wall and the lung (the pleural cavity).

Henoch-Schonlein purpura is a disease that involves purple spots on the skin, joint pain, gastrointestinal problems, and (a type of kidney disorder).

The term “hepatic” refers to the liver. For example, the hepatic duct drains bile from the liver.

Hepatic encephalopathy is a worsening of brain function that occurs when the liver is no longer able to remove toxic substances in the blood.

A hepatic hemangioma is a noncancerous liver made of widened (dilated) blood vessels.

Hepatic ischemia is a condition in which the liver does not get enough blood or oxygen, causing injury to liver cells.

Hepatic vein obstruction is a blockage of the vein, which carries blood away from the liver.

Hepatitis is swelling and inflammation of the liver. It is not a condition, but is often used to refer to a viral infection of the liver.

Hepatitis A is inflammation (irritation and swelling) of the liver from the hepatitis A virus. See also:

The hepatitis A vaccine protects you against a type of liver infection called . The vaccine will not protect you from other types of hepatitis.

Hepatitis B is irritation and swelling (inflammation) of the liver due to infection with the hepatitis B virus (HBV). Other types of viral hepatitis include: See also: Chronic persistent hepatitis

The hepatitis B vaccine protects against hepatitis B, a serious viral disease that damages the liver. This vaccine is one of the recommended childhood immunizations, but many adults also need to be vaccinated.

Hepatitis C is a viral disease that leads to swelling (inflammation) of the liver.

The hepatitis virus panel is a series of blood tests used to detect current or past infection by , , or . It can screen blood samples for more than one kind of hepatitis virus at the same time. and tests can detect each of the different hepatitis viruses. Note: Hepatitis D only causes disease ...

Hepatocellular carcinoma is cancer of the liver.

Hepatocerebral degeneration is a brain disorder that occurs in people with liver damage.

Hepatomegaly is swelling of the liver beyond its normal size. If both the liver and spleen are enlarged, it is called hepatosplenomegaly. See also:

Hepatorenal syndrome is a condition in which there is progressive kidney failure in a person with of the liver. It is a serious and often life-threatening complication of cirrhosis.

Hereditary amyloidosis is a condition in which abnormal deposits (called amyloid) form in almost every tissue in the body. These protein deposits damage the tissues and interfere with the function of the involved organs.

Hereditary angioedema is a rare but serious problem with the immune system that is passed down through families. It causes swelling, particularly of the face and airways, and abdominal cramping. See also:

Hereditary elliptocytosis is a disorder passed down through families in which the red blood cells are abnormally shaped. See also:

Hereditary fructose intolerance is a disorder in which a person lacks the protein needed to break down fructose. Fructose is a fruit sugar that naturally occurs in the body. Man-made fructose is used as a sweetener in many foods, including baby food and drinks.

Hereditary ovalocytosis is rare condition passed down through families (inherited) in which blood cells are slightly oval-shaped instead of round. It is a form of .

Hereditary urea cycle abnormality is an inherited condition that can cause problems with the removal of waste from the body in the urine.

A hernia is usually a sac formed by the lining of the abdominal cavity (peritoneum). The sac comes through a hole or weak area in the fascia, the strong layer of the abdominal wall that surrounds the muscle. The types of hernias are based on where they occur: appears as a bulge in the upper thigh. ...

A herniated (slipped) disk occurs when all or part of a spinal disk is forced through a weakened part of the disk. This places pressure on nearby nerves. See also:

Heroin is an illegal street drug that is very addictive. This article discusses overdose due to heroin. An is when you take more than the normal or recommended amount of something, usually a drug. An overdose may result in serious, harmful symptoms or death. This is for information only and not ...

Herpangina is a viral illness in which ulcers and sores (lesions) form inside the mouth, and there is a sore throat and fever. See also:

Herpes esophagitis is a viral infection that involves inflammation and in the esophagus, the tube that carries food from the mouth to the stomach.

Herpes labialis is infection of the lips, mouth, or gums with the virus. It leads to the development of small, painful commonly called cold sores or fever blisters.

Herpes simplex is a viral infection that mainly affects the mouth or genital area.

Herpes viral culture of a lesion is a laboratory test to check if a skin sample is infected with the herpes simplex virus. See also: (cold sores)

Herpetic stomatitis is a viral infection of the mouth that causes ulcers and inflammation. These mouth ulcers are not the same as canker sores, which are caused by a different virus.

Heterochromia is the presence of different colored eyes in the same person.

Hiatal hernia is a condition in which a portion of the stomach protrudes upward into the chest, through an opening in the diaphragm. The diaphragm is the sheet of muscle that separates the chest from the abdomen. It is used in breathing.

The HiB vaccine (immunization) prevents childhood Haemophilus influenzae B infections, which can cause severe and potentially deady illnesses that affect the brain, lungs, and bones or joints.

A hiccup is an unintentional movement (spasm) of the diaphragm, the muscle at the base of the lungs. The spasm is followed by quick closing of the vocal cords, which produces a distinctive sound.

High arch is an arch that is raised more than normal. The arch, or instep, runs from the toes to the heel on the bottom of the foot. It is also called pes cavus. High arch is the opposite of .

The medical term for high blood cholesterol and triglycerides is lipid disorder. Such a disorder occurs when you have too many fatty substances in your blood. These substances include cholesterol and .

High blood pressure (hypertension) is an increase in the force of blood against the arteries in the body. This article focuses on high blood pressure in infants.

Hip fracture surgery is done to repair a break in the upper part of the thigh bone. The thigh bone is called the femur. It is part of the hip joint. See also:

Hip joint replacement is surgery to replace all or part of the hip joint with an artificial joint. The artificial joint is called a .

Hip pain involves any pain in or around the hip joint.

Hirschsprung’s disease is a blockage of the large intestine due to improper muscle movement in the bowel. It is a congenital condition, which means it is present from birth.

His bundle electrography is a test that measures electrical activity in a part of the heart that carries the signals that control the time between heartbeats (contractions).

A histiocyte is a type of immune cell that eats foreign substances in an effort to protect the body from infection.

Histiocytosis is a general name for a group of syndromes that involve an abnormal increase in the number of immune cells called . There are three major classes of histiocytoses: Langerhans cell histiocytosis, which is also called histiocytosis X Malignant histiocytosis syndrome (now known as ...

A histocompatibility antigen blood test looks at proteins called human leukocyte antigens (HLAs), which are found on the surface of nearly every cell in the human body. HLAs are found in large amounts on the surface of white blood cells. They help the immune system tell the difference between body ...

Histoplasma complement fixation is a blood test that checks for signs of infection due to a fungus called Histoplasma capsulatum (H. capsulatum). Some people who breathe in particles of this fungus may get an infection called . See also:

Histoplasma skin test is a method to check if you have been exposed to a fungus called Histoplasma capsulatum. The fungus causes an infection called .

Histoplasmosis is an infection due to the Histoplasma capsulatum fungus.

Acute pulmonary histoplasmosis is a respiratory infection caused by inhaling the of the fungus Histoplasma capsulatum.

Chronic pulmonary histoplasmosis is a long-term respiratory infection caused by breathing the spores of the fungus, Histoplasma capsulatum. See also:

Disseminated histoplasmosis is a fungal infection that occurs after inhaling the of the fungus Histoplasma capsulatum. See also:

Histrionic personality disorder is a condition in which people act in a very emotional and dramatic way that draws attention to themselves.

HIV infection is a condition caused by the human immunodeficiency virus (HIV). The condition gradually destroys the immune system, which makes it harder for the body to fight infections. This article provides a general overview. For more detailed information, see:

Hives are raised, often itchy, red welts on the surface of the skin. They are usually an allergic reaction to food or medicine.

HLA-B27 is a blood test to look for specific protein found on the surface of white blood cells. The protein is called human leukocyte antigen B27 (HLA-B27). Human leukocyte antigens (HLAs) are proteins that help the body’s immune system tell the difference between its own cells and foreign, ...

Hoarseness is having difficulty producing sound when trying to speak, or a change in the pitch or quality of the voice. The voice may sound weak, very breathy, scratchy, or husky.

Hodgkin’s lymphoma is a cancer of lymph tissue found in the lymph nodes, spleen, liver, bone marrow, and other sites.

A Holter monitor is a machine that continuously records the heart’s rhythms. The monitor is usually worn for 24 – 48 hours during normal activity. See also .

A home apnea monitor is a portable machine used to monitor a baby’s heart beat and breathing after coming home from the hospital. When the baby has a heart rate or breathing rate that is below the limits set on the monitor, an alarm goes off. The monitor is smaller and less complex than ...

Home vision tests measure the ability to see fine detail.

Homocystinuria is an inherited disorder that affects the of the methionine.

Hookworm is a roundworm infestation affecting the small intestine and lungs. The worms are about 1/2 inch long.

Hormonal effects in newborns occur because, while they are in the womb, babies are exposed to many chemicals (hormones) present in the mother’s bloodstream. After birth, the infants are no longer exposed to these hormones. This exposure may cause temporary conditions in a newborn.

Blood or urine tests can determine the levels of various hormones in the body. This includes reproductive hormones, thyroid hormones, adrenal hormones, pituitary hormones, and many others. For more information, see:

Hormone therapy (HT) uses one or more female hormones, commonly estrogen and progestin and sometimes testosterone, to treat symptoms of . Symptoms of menopause include hot flashes, vaginal dryness, mood swings, sleep disorders, and decreased sexual desire. Hormone therapy comes as a pill, patch, ...

Horner syndrome is a rare condition that affects the nerves to the eye and face.

Hospital-acquired pneumonia is an infection of the lungs contracted during a hospital stay.

Hot tub is an infection of the hair follicles that occurs when you come into contact with certain bacteria that live in warm, wet areas.

Most household glues, such as Elmer’s glue, are not poisonous. However, household glue poisoning can occur when someone intentionally breathes in glue fumes in an attempt to get “high.” This is for information only and not for use in the treatment or management of an actual ...

A sling is a device used to support and keep still (immobilize) an injured part of the body. Slings can be used for many different injuries, but are most often used when you have a broken (fractured) or dislocated arm or shoulder. See also:

A splint is a device used for holding a part of the body stable and motionless to decrease pain and prevent further injury.

The HPV vaccine protects against infection by certain strains of the human papilloma virus (HPV) that can cause cervical cancer and genital warts. HPV spreads mostly through sexual contact. Almost all cervical cancers are caused by HPV. HPV vaccination is expected to prevent about 70% of cervical ...

Human bites are usually caused by one person biting another, although they may result from a situation in which one person comes into contact with another person’s teeth. In a fight, for example, one person’s knuckles may come into contact with another person’s teeth, and if the ...

Human placental lactogen (hPL) is a hormone produced by the placenta, the organ that develops during pregnancy to help feed the growing baby. This hormone breaks down fats from the mother to provide fuel for the the growing baby. It can lead to insulin resistance and carbohydrate intolerance in the ...

Hump behind the shoulders is a lump of fat on the back of the neck.

Hunter syndrome is an inherited disease in which long chains of sugar molecules () are not broken down correctly and build up in the body.

Huntington’s disease is a disorder passed down through families in which certain nerve cells in the brain waste away, or degenerate.

Hurler syndrome is a rare, inherited disease of in which a person cannot break down long chains of sugar molecules called glycosaminoglycans (formerly called mucopolysaccharides). Hurler syndrome belongs to a group of diseases called mucopolysaccharidoses, or MPS. See also:

A hydatidiform mole is a rare mass or growth that forms inside the uterus at the beginning of a pregnancy. It is a type of gestational trophoblastic disease (GTD). See also: (a cancerous form of GTD)

Hydrocarbon pneumonia is caused by drinking or breathing in , , , paint thinner, or other oily materials or solvents. These products cause fairly rapid changes in the lungs, including inflammation, swelling, and bleeding. This is for information only and not for use in the treatment or management ...

A hydrocele is a fluid-filled sack along the spermatic cord within the .

Hydrocele repair is surgery to correct the swelling of the that occurs when you have a hydrocele. A is the backup of fluid in a testicle. Baby boys sometimes have a hydrocele at birth. Hydroceles also occur in older boys and men. Sometimes they form when there is also a hernia (an abnormal ...

Hydrocephalus is a buildup of fluid inside the skull, leading to brain swelling. Hydrocephalus means “water on the brain.”

Hydrocholoric acid is a clear, poisonous liquid. It is highly corrosive, which means it immediately causes severe damage, such as burning, on contact. This article discusses poisoning due to swallowing or breathing in hydrochloric acid. This is for information only and not for use in the ...

Hydrocodone and acetaminophen overdose occurs when someone accidentally or intentionally takes more than the normal or recommended amount of a painkiller containing both the opioid medication, hydrocodone, and acetaminophen (Tylenol). This is for information only and not for use in the treatment ...

Hydrocodone and oxycodone are drugs that are mostly used to treat extreme pain. Hydrocodone/oxycodone overdose occurs when someone intentionally or accidentally take too much medicine containing these ingredients. A person may accidentally take too much of the medicine because they are not getting ...

Hydrofluoric acid is a very strong inorganic acid. This article discusses poisoning from swallowing, breathing in, or touching hydrofluoric acid. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your ...

Hydrogen peroxide is a liquid commonly used to fight germs. Hydrogen peroxide poisoning occurs when large amounts of the liquid come in contact with the lungs or eyes. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, ...

Hydromorphone is a prescription medicine used to relieve severe pain. Hydromorphone occurs when someone accidentally or intentionally takes more than the normal or recommended amount of this medication. This is for information only and not for use in the treatment or management of an actual ...

Hydrops fetalis is a serious condition in which abnormal amounts of fluid build up in two or more body areas of a fetus or newborn. See also:

Hydroxyzine is an antihistamine used to treat symptoms of allergies and motion sickness. Hydroxyzine occurs when someone accidentally or intentionally takes more than the normal or recommended amount of this medication. This is for information only and not for use in the treatment or management ...

Hymenolepiasis is infestation by one of two species of : Hymenolepis nana or Hymenolepis diminuta.

Hyperactivity is a state of too much muscle activity. This term is also used to describe a situation when a particular portion of the body is too active, such as when a gland produces too much of its particular hormone. See also:

Hyperactivity refers to increased movement, impulsiveness, distractibility, and decreased attention span. A popular but controversial belief is that children are more likely to be hyperactive if they eat sugar, artificial sweeteners, or certain food colorings. This article focuses on the possible ...

Primary and secondary hyperaldosteronism are conditions in which the adrenal gland releases too much of the hormone .

Hyperbaric oxygen therapy uses a special chamber, sometimes called a pressure chamber, to increase the amount of oxygen in the blood.

Hypercalcemia is too much calcium in the blood.

Hypercoagulable state is a condition in which you are more likely to develop . Blood clots can develop in either arteries or veins. See also: (DVT) (Budd-Chiari syndrome)

Hyperelastic skin is skin that can be stretched beyond what is considered normal, and then returns to normal.

Hyperemesis gravidarum is extreme, persistent nausea and vomiting during pregnancy that may lead to .

Hyperglycemia is abnormally high blood sugar. This article discusses hyperglycemia in infants.

Hyperhidrosis is a medical condition in which a person sweats excessively and unpredictably. People with hyperhidrosis may sweat even when the temperature is cool or when they are at rest.

Hyperimmunization is the presence of a larger-than-normal number of to a specific . This creates a state of greater than normal. Immune system overactivity can cause many different diseases.

Hyperimmunoglobulin E syndrome is a rare, inherited disease associated with abnormalities of the skin, sinuses, lungs, bones, and teeth.

Hyperkalemia is higher-than-normal levels of potassium in the blood.

Hyperkalemic periodic paralysis is a disorder that involves occasional episodes of and, sometimes, higher than normal levels of potassium in the blood. It is one of a group of genetic disorders that includes and .

Hypermobile joints are joints that move beyond the normal range with little effort. Joints most commonly affected are the elbows, wrists, fingers, and knees.

Hyperparathyroidism is excessive production of parathyroid hormone (PTH) by the parathyroid glands. See also:

Hyperplasia is increased cell production in a normal tissue or organ. Hyperplasia may be a sign of precancerous changes. This is called pathologic hyperplasia. It can also be due to the growth of completely normal cells. This is called physiologic hyperplasia.

Hypersensitivity pneumonitis is inflammation of the lungs due to breathing in a foreign substance, usually certain types of dust, fungus, or molds.

Hypersplenism is a condition in which the spleen is overactive.

Hypertension is the term used to describe high blood pressure. Blood pressure is a measurement of the force against the walls of your arteries as the heart pumps blood through the body. Blood pressure readings are measured in millimeters of mercury (mmHg) and usually given as two numbers — ...

Hypertensive heart disease refers to heart problems that occur because of high blood pressure. These problems include: Thickening of the heart muscle See also:

Hypertensive retinopathy is damage to the from high blood pressure. The retina is the layer of tissue at the back part of the eye. It changes light and images that enter the eye into nerve signals that are sent to the brain. See also:

Hyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often referred to as an “overactive thyroid.”

Hypertrophic cardiomyopathy (HCM) is a condition in which the heart muscle becomes thick. The thickening makes it harder for blood to leave the heart, forcing the heart to work harder to pump blood.

Hyperventilation is rapid or deep breathing that can occur with anxiety or panic. It is also called overbreathing, and may leave you feeling breathless. See also:

Hyperviscosity of the newborn is the slowing and blockage of blood flow that results when there are too many red blood cells in an infant’s blood.

Hypervitaminosis A is having too much in the body.

Hypervitaminosis D is a condition that occurs after taking excessive doses of .

Hyphema is blood in the front area of the eye.

Hypnotics are medications that cause sleep or partial loss of consciousness.

Hypocalcemia is an abnormally low blood calcium level. This article discusses low blood calcium levels in infants.

Hypochondria is a belief that physical symptoms are signs of a serious illness, even when there is no medical evidence to support the presence of an illness.

Hypochromia means that the red blood cells have less color than normal when examined under a microscope. This usually occurs when there is not enough of the pigment that carries oxygen () in the red blood cells. The most common cause of hypochromia in the United States is iron deficiency. The ...

Hypoglycemia is a condition that occurs when your blood sugar (glucose) is too low. Blood sugar below 70 mg/dL is considered low. Blood sugars at this level can harm you.

Hypogonadism is when the sex glands produce little or no hormones. In men, these glands (gonads) are the testes; in women, they are the ovaries.

Hypogonadotropic hypogonadism is absent or decreased function of the male or the female ovaries. It is considered a form of secondary hypogonadism, which means the condition is due to a problem with the pituitary or hypothalamus gland. See also:

Hypokalemia is a lower-than-normal amount of potassium in the blood.

Hypokalemic periodic paralysis is an inherited disorder that causes occasional episodes of muscle weakness. It is one of a group of genetic disorders that includes and .

Hypomagnesemia means low levels of magnesium in the blood.

Hyponatremia is a metabolic condition in which there is not enough sodium (salt) in the body fluids outside the cells.

Hypoparathyroidism is is an endocrine disorder in which the parathyroid glands in the neck do not produce enough parathyroid hormone (PTH). See also:

Hypophosphatemia is a low level of in the blood.

Hypopituitarism is a condition in which the pituitary gland does not produce normal amounts of some or all of its hormones.

Hypoplastic left heart syndrome occurs when parts of the left side of the heart (mitral valve, left ventricle, aortic valve, and aorta) do not develop completely. The condition is congenital (present at birth).

Hypospadias is a birth (congenital) defect in which the opening of the urethra is on the underside, rather than at the end, of the penis. See also:

Hypospadias repair is surgery to correct a birth defect in boys in which the urethra (the tube that carries urine from the bladder to outside the body) does not end at the tip of the . Instead, it ends on the underside. In more severe cases, the urethra opens at the middle or bottom of the penis, or ...

Low blood pressure, or hypotension, occurs when blood pressure during and after each heartbeat is much lower than usual. This means the heart, brain, and other parts of the body do not get enough blood. See also:

Hypothalamic dysfunction is a problem with the region of the brain called the , which helps control the pituitary gland and regulate many body functions.

A hypothalamic is an abnormal growth in the gland, which is located in the brain.

The hypothalamus is an area of the brain that produces hormones that control: Body temperature Hunger Moods Release of hormones from many glands, especially the pituitary gland Sex drive Sleep Thirst

Hypothermia is dangerously low body temperature, below 95 °F (35 °C).

Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. See also: Chronic thyroiditis ()

Hypotonia means decreased muscle tone.

Hypoventilation is too shallow or too slow breathing, which does not meet the needs of the body. It may also refer to reduced lung function. If a person hypoventilates, the body’s carbon dioxide level rises, which results in too little oxygen in the blood.

Hypovolemic is an emergency condition in which severe blood and fluid loss makes the heart unable to pump enough blood to the body. This type of shock can cause many organs to stop working.

A hysterectomy is surgery to remove a woman’s uterus. It may be done through an incision (cut) in either the abdomen (belly) or the .

Hysterosalpingography is an x-ray of the uterus and fallopian tubes that involves the injection of contrast (dye) through the cervix.