A disease is an abnormal condition that negatively affects the structure or function of all or part of an organism, not caused immediately by external injury. It is typically associated with specific signs and symptoms and can be caused by external factors like pathogens or internal dysfunctions such as immune system disorders

. There are four main types of diseases:

• Infectious diseases: caused by pathogenic microorganisms such as viruses, bacteria, fungi, and parasites, and can be contagious or communicable.
• Deficiency diseases: caused by a lack of essential nutrients.
• Hereditary diseases: caused by genetic mutations, which can be inherited or arise spontaneously.
• Physiological diseases: related to internal dysfunctions of body systems

Diseases can also be classified as acute (short-term), chronic (long-lasting), congenital (present at birth), genetic, iatrogenic (caused by medical treatment), idiopathic (unknown cause), incurable, primary (root cause), or secondary (complication of another disease)

. Noncommunicable diseases, which are not transmissible between people, include cancer, cardiovascular diseases, chronic respiratory diseases, and diabetes. These often develop slowly and can be influenced by genetic and environmental factors

. In summary, a disease is any condition that impairs normal bodily function, caused by a variety of factors including infections, genetics, lifestyle, and environmental exposures