A non-communicable disease is not infectious, which means it cannot pass — or communicate — between individuals. The term "disease" may be defined as any disorder of the body or impairment of its functioning. This means that the types of non-communicable disease include injury and congenital abnormalities. Classic examples of these diseases are cancer, cardiovascular illnesses, mental health disorders, and dysfunctions of the respiratory system.
Varying estimates of the worldwide incidence of non-communicable disease show that it is approximately equal to communicable disease incidence statistics. In some parts of the world, contagious illnesses are more common. Developing countries are likely to have this pattern because they may lack measures, like clean water sources, that minimize the spread of infectious illnesses. In these environments, epidemics of serious communicable diseases occur with greater regularity, and they may severely impact population levels.
In contrast, equal or at least elevated rates of non-communicable diseases are more likely to occur in developed countries. People with longer lifespans are at greater risk for developing disease associated with age. For example, prostate cancer generally occurs in older men. Illnesses like heart disease and dementia also have a greater impact in older populations.
Moreover, aging people are prone to greater non-communicable disease because of early lifestyle choices. Some of these choices might include drinking excessively, engaging in unsafe sexual behavior, overeating, and smoking. Certain lifestyle choices, however, may reduce the risk for illnesses; for example, having children early and breastfeeding them may reduce risk for breast cancer.
The types and characteristics of non-communicable disease can vary. Many illnesses, like cancer, heart disease or certain autoimmune conditions, exist for a long time and may progressively worsen. A person’s susceptibility to non-contagious disorders may have genetic components, as is the case with some reproductive tract cancers, certain mental illnesses, and many congenital defects.
The illnesses that are classified as non-communicable diseases are often clearly delineated from contagious disorders. No one "catches" an injury or contracts a birth defect from someone else. These diseases are or aren’t present, and they can’t be passed to other people.
In other instances, the definition of a non-communicable disease has some noted gray areas. Illnesses like cervical cancer can’t be passed to others, but they are frequently caused by an infection with communicable forms of human papillomavirus. Post-herpetic neuralgia isn’t contagious, but it is a complication of shingles, which is the body’s reaction to chicken pox contagion many years earlier.
Another ambiguous area relates to diseases that are attributed to lifestyle. Obesity is thought to be "contagious" to close family members and friends because shared eating or leisure habits can support weight gain. Illnesses like alcoholism and some eating disorders may be socially encouraged among certain population groups. Occasionally, suicides, especially of children and young adults, come in waves and are influenced by each other.