In medicine, disease is a medical condition that impairs the body’s normal homeostatic processes and manifests in signs and symptoms. These include pain, dysfunction, distress and/or death to the affected individual and problems for those who interact with him or her.
Many diseases are caused by microorganisms, usually germs such as bacteria, viruses, protozoa, and fungi. Some diseases spread from one person to another by direct contact (like hand-to-hand contact), while others spread by infecting food or water, or through bites of insects or other animals. Many diseases can be prevented by vaccinations or by avoiding contact with the microorganisms that cause them.
Other diseases are not infectious, and do not involve any damage to the body or mind. These include some forms of cancer, heart disease, and genetic disease such as diabetes. Some non-infectious diseases can also be controlled or even prevented by diet, exercise, and lifestyle changes.
Some diseases are incurable, and even treatment may not cure the condition. However, a cure can provide significant improvements in health and quality of life, such as reductions in the severity of symptoms and the need for follow-up visits with doctors or other healthcare providers.
The study of disease is called epidemiology and involves studying patterns of illness in groups of people. Epidemiologists use this information to make recommendations for prevention and control of disease.