Health Library

Obesity is a term used to describe body weight that is much greater than what is healthy. If you are obese, you also have a much higher amount of body fat than is healthy or desirable. Adults with a (BMI, calculated as weight in kilograms divided by height in meters squared) between 25 kg/m2 and ...

Obesity hypoventilation syndrome (OHS) is a condition that occurs in obese people, in which poor breathing leads to lower oxygen levels and higher carbon dioxide levels in the blood.

Obsessive-compulsive disorder is an anxiety disorder in which people have unwanted and repeated thoughts, feelings, ideas, sensations (obsessions), or behaviors that make them feel driven to do something (compulsions). Often the person carries out the behaviors to get rid of the obsessive ...

Obsessive-compulsive personality disorder (OCPD) is a condition in which a person is preoccupied with rules, orderliness, and control.

Obstructive sleep apnea is a condition in which pauses in breathing occur during sleep because the airway has become narrowed, blocked, or floppy. A pause in breathing is referred to as an apnea episode. Almost everyone has brief apnea episodes while they sleep. This article discusses ...

Obstructive uropathy is a condition in which the flow of urine is blocked, causing it to back up and injure one or both kidneys.

Occupational asthma is a lung disorder in which various substances found in the workplace lead to breathing difficulties. See also:

Occupational hearing loss is damage to the inner ear from noise or vibrations due to certain types of jobs or entertainment.

Oil-based paint poisoning occurs when large amounts of oil-based paint get into your stomach or lungs. It may also occur if the poison gets into your eyes or touches your skin. This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an ...

Oleander poisoning occurs when someone sucks nectar from the flowers or chews leaves from the oleander or yellow oleander plant. Poisoning can also happen if you eat honey made by bees that used the oleander plant for nectar. This is for information only and not for use in the treatment or ...

Olivopontocerebellar atrophy is a disease that causes areas deep in the brain, just above the spinal cord, to shrink.

An omphalocele is a birth defect in which the infant’s intestine or other abdominal organs stick out of the belly button (navel). In babies with an omphalocele, the intestines are covered only by a thin layer of tissue and can be easily seen. An omphalocele is a type of hernia. Hernia means ...

Omphalocele repair is surgery to repair a birth defect in the wall of the belly (abdomen) in which all or parts of the small intestine, liver, and large intestine stick out of the belly button (navel) in a thin sac. Other birth defects are also present. See also: (a similar defect)

Open heart surgery is any surgery where the chest is opened and surgery is performed on the heart muscle, valves, arteries, or other heart structures (such as the aorta). The term “open” means that the chest is “cut” open. A heart-lung machine (also called cardiopulmonary ...

An open is surgery to remove a small piece of tissue from the lung. The sample is then examined for , infection, or .

An open pleural biopsy is a procedure to remove and examine the tissue that lines the inside of the chest. This tissue is called the pleura.

Ophthalmoscopy is an examination of the back part of the eye (fundus), which includes the , optic disc, , and blood vessels.

Opiate withdrawal refers to the wide range of symptoms that occur after stopping or dramatically reducing opiate drugs after heavy and prolonged use (several weeks or more). Opiate drugs include heroin, morphine, codeine, Oxycontin, Dilaudid, methadone, and others.

Opium and its forms (which include morphine, heroin, oxycodone, and the synthetic opioid narcotics) lead to an abnormal mental state, which generally involves excessive or .

Opisthotonos is a condition in which the body is held in an abnormal posture. It usually involves rigidity and severe arching of the back, with the head thrown backward. If a person with opisthotonos lies on his or her back, only the back of the head and the heels would touch the supporting ...

Oppositional defiant disorder is a pattern of disobedient, hostile, and defiant behavior toward authority figures.

Gliomas are tumors that grow in various parts of the brain. Optic gliomas can affect: One or both of the optic nerves, which carry visual information to the brain from each eye The optic chiasm, the area where the optic nerves cross each other in front of the hypothalamus of the brain An optic ...

Optic nerve atrophy is damage to the optic nerve. The optic nerve carries images of what we see from the eye to the brain.

Optic neuritis is inflammation of the optic nerve. It may cause sudden, reduced vision in the affected eye.

Oral cancer is cancer of the mouth.

Oral hypoglycemic pills are a class of prescription medications used to control diabetes. Oral means “taken by mouth.” There are many different types of oral hypoglycemics. This article focuses on a class called sulfonylureas. An occurs when someone accidentally or intentionally takes ...

A computed tomography (CT) scan of the orbit is an imaging method that uses x-rays to create detailed pictures of the eye sockets (orbits) and eyes. See:

Orbital cellulitis is an infection of the tissues immediately surrounding the eye, including the eyelids, eyebrow, and cheek.

Orbital pseudotumor is a swelling of the tissues behind the eye in an area called the orbit. The orbit is the bony cavity in the skull where the eye sits. It protects the eyeball and the muscles and tissue that surround it. Unlike cancerous tumors, an orbital pseudotumor does not spread to other ...

Orchitis is swelling (inflammation) of one or both of the .

Organic brain syndrome (OBS) is a general term used to describe decreased mental function due to a medical disease, other than a psychiatric illness. It is often used synonymously (but incorrectly) with .

An oropharynx lesion biopsy is surgery in which tissue from an abnormal growth or mouth sore is removed and checked for problems.

Orthopedics, or orthopedic services, is the medical specialty that involves the treatment of the musculoskeletal system, which is made up of your body’s bones, joints, ligaments, tendons, and muscles.

Osgood-Schlatter disease is a painful swelling of the bump on the upper part of the shinbone, just below the knee. This bump is called the anterior tibial tubercle.

Osler-Weber-Rendu syndrome is an inherited disorder of the blood vessels that can cause excessive bleeding.

Osmality is a test that measures the concentration of all chemical particles found in the fluid part of blood.

The osmolality urine test the concentration of particles in urine. Osmolality (particles/kg water) and osmolarity (particles/liter of solution) are sometimes confused, but for dilute fluids such as urine they are essentially the same. A blood test may also be done to measure osmolality. See:

Osmotic diuresis is increased urination due to the presence of certain substances in the fluid filtered by the kidneys. (This fluid eventually becomes urine.)

Osmotic fragility is a test to detect whether red blood cells are more likely to break down.

Osteitis fibrosa is a complication of in which the bones turn soft and become deformed.

Osteoarthritis (OA) is the most common joint disorder.

Osteogenesis imperfecta is a condition causing extremely fragile bones.

Osteomalacia is softening of the bones due to a lack of or a problem with the body’s ability to break down and use this vitamin.

Osteomyelitis is an or bone infection.

Osteonecrosis is bone death caused by poor blood supply to the area. It is most common in the hip and shoulder.

Osteopenia is a decrease in the amount of calcium and phosphorus in the bone. This can cause bones to be weak and brittle, and increases the risk for broken bones.

Osteoporosis is the thinning of bone tissue and loss of bone density over time.

Osteosarcoma is a cancerous (malignant) that usually develops during the period of rapid growth that occurs in adolescence, as a teenager matures into an adult.

Otitis is a general term for infection or inflammation of the ear.

Otitis media with effusion (OME) is when there is thick or sticky fluid behind the eardrum in the middle ear, but there is no .

Otosclerosis is an abnormal bone growth in the middle ear that causes .

Ovarian cancer is cancer that starts in the ovaries. The ovaries are the female reproductive organs that produce eggs.

An ovarian cyst is a sac filled with fluid that forms on or inside of an ovary. This article is about cysts that form during your monthly menstrual cycle, called functional cysts. Functional cysts are not the same as cysts caused by cancer or other diseases. For more information about other ...

Ovarian hyperstimulation syndrome (OHSS) is a complication occasionally seen in women who take certain fertility medicines that stimulate egg production. See also:

Ovarian hypofunction is reduced function of the ovaries (including decreased production of hormones).

Ovarian overproduction of androgens is a condition in which the female ovaries make too much . This leads to the development of male characteristics in a woman. Other hormones, called androgens, from other parts of the body can also cause the development of male characteristics in women.

This article discusses the harmful effects from swallowing or breathing in an oven cleaner. 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 ...

Over-the-counter birth control methods are used during sex to avoid pregnancy and sometimes to prevent sexually transmitted infections (STIs). Over-the-counter means that they can be purchased by anyone, without a doctor’s prescription. For more information about birth control options, see:

Common problems may occur during breastfeeding. Fortunately, most problems can be easily managed with a variety of strategies. Moms who breastfeed their babies may feel confused by a lack of experience or support. They may be afraid or ashamed to ask for help for such a “natural” ...

An overdose 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. If you take too much of something on purpose, it is called an intentional or deliberate overdose. If the overdose happens by ...

Nearly two-thirds of the United States population is overweight. There are many ways to determine if a person is overweight, but experts believe that a person’s body mass index (BMI) is the best way to assess an adult’s weight in relation to their height. A BMI between 18.5 and 24.9 is ...

Oxalic acid is a poisonous, colorless substance. This article discusses poisoning from swallowing oxalic 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 local emergency number (such as ...

Oxazepam is a medicine used to treat anxiety and symptoms of alcohol withdrawal. Oxazepam overdose occurs when someone accidentally or intentionally takes too much of this medicine. This is for information only and not for use in the treatment or management of an actual poison exposure. If you ...

Oxygen is a gas that the cells in your body need to work properly. The air we breathe normally has 21% oxygen. A maximum of 100% oxygen can be given. WHY IS OXYGEN USED? Babies with heart or lung problems may need increased amounts of oxygen. HOW IS OXYGEN DELIVERED? There are several ...

Ozena is a disease of the nose in which there is a a wasting away of the bony ridges and internal mucous membranes. Nasal crusting, discharge, and a very bad smell are other usual symptoms of ozena. Ozena may develop after a long period of nasal swelling. Ozena is also called atrophic ...