Disease is any condition that results in the malfunctioning of a body part or system. Diseases can be caused by a wide variety of factors, including infection, genetic abnormalities, environmental exposure, and lifestyle choices. Some diseases are acute, lasting only a short time, while others are chronic, lasting for months or years. Many diseases can be managed with medication and lifestyle changes, but some require more invasive treatments, such as surgery.
Diseases can be classified in a number of ways. The most common method is by cause: infectious diseases are caused by pathogens such as bacteria or viruses; genetic diseases are caused by abnormalities in genes or chromosomes; and degenerative diseases occur when cells break down over time. Diseases can also be classified by the body system affected: cardiovascular diseases affect the heart and blood vessels; respiratory diseases affect the lungs; and so on.
There are many different types of disease, ranging from relatively mild conditions to life-threatening illnesses. Common examples include colds and flu (respiratory infections), arthritis (a degenerative disease), and cancer (a neoplastic disease). Less common examples include autoimmune disorders such as lupus erythematosus (an inflammatory disease) and cystic fibrosis (a hereditary disorder).