DEFINITION Neurodermatitis starts with a patch of itchy skin, but scratching it makes the area even itchier. Eventually you may scratch simply out of habit. This cycle of chronic itching and scratching can cause the affected skin to become thick…
DEFINITION Neuroblastoma is a cancer that develops from immature nerve cells found in several areas of the body. Neuroblastoma most commonly arises in and around the adrenal glands, which have similar origins to nerve cells and sit atop the kidneys.…
DEFINITION A nightmare is a disturbing dream associated with negative feelings, such as anxiety or fear. Nightmares are common, and occasional nightmares usually are nothing to worry about. However, they may become a problem if you have them often and…
DEFINITION Nonalcoholic fatty liver disease is a term used to describe the accumulation of fat in the liver of people who drink little or no alcohol. Nonalcoholic fatty liver disease is common and, for most people, causes no signs and…
DEFINITION Tapeworm infection is caused by ingesting food or water contaminated with tapeworm eggs or larvae. If you ingest certain tapeworm eggs, they can migrate outside your intestines and form larval cysts in body tissues and organs (invasive infection). If…
DEFINITION Odontogenic lesions are cysts or tumors that develop in your jawbone or the soft tissues in your mouth. Odontogenic lesions can vary greatly in size and severity. These lesions are usually noncancerous (benign), but they may behave aggressively at…
DEFINITION Ocular rosacea is inflammation that causes redness, burning and itching of the eyes. It often develops in people who have rosacea, a chronic skin condition that affects the face. Sometimes ocular, or eye, rosacea is the first sign that…
DEFINITION Obsessive-compulsive disorder (OCD) is characterized by unreasonable thoughts and fears (obsessions) that lead you to do repetitive behaviors (compulsions). It’s also possible to have only obsessions or only compulsions and still have OCD. With OCD, you may or may…
DEFINITION Obesity is a complex disorder involving an excessive amount of body fat. Obesity isn’t just a cosmetic concern. It increases your risk of diseases and health problems, such as heart disease, diabetes and high blood pressure. Being extremely obese…
DEFINITION Norovirus infection can cause the sudden onset of severe vomiting and diarrhea. The virus is highly contagious and commonly spread through food or water that is contaminated by fecal matter during preparation. You can also be infected through close…
DEFINITION Nonmelanoma skin cancer refers to all the types of cancer that occur in the skin that are not melanoma. Several types of skin cancer fall within the broader category of nonmelanoma skin cancer, with the most common types being…
DEFINITION Non-Hodgkin’s lymphoma, also called non-Hodgkin lymphoma, is cancer that originates in your lymphatic system, the disease-fighting network spread throughout your body. In non-Hodgkin’s lymphoma, tumors develop from lymphocytes — a type of white blood cell. Non-Hodgkin’s lymphoma is more…