Individuals live and continuously interact with their living and nonliving environment and the factors that can potentially affect the health of a person in a negative way are called **risk factors**. Risk factors increase the chance of an individual acquiring disease or infection. Some of the environmental factors that be a *risk factors* are air, water, waste, landfills, and solar radiation.

To help your immune system to function properly, effectively, and efficiently, healthful behaviors such as eating healthy, getting plenty of rest and exercise, and refraining oneself from harmful activities are needed. These behaviors reduce the exposure of an individual to diseases and infections.

**Cancer** is a life-threatening disease that is characterized by the presence of abnormal and uncontrollable cell growth and reproduction. Cancer is a unique type of disease because the causative agent is not a foreign cell or material but rather the body’s own cell machinery.

Cancer diseases are commonly caused by mutations or defects in the genetic make-up of an individual, specifically in the genes that control cell growth and reproduction. There are several agents that can lead to cancer:

1. Inherited defective genes
2. Viral vectors that can cause mutation in the cell’s machinery.
3. Carcinogens (chemicals that can cause mutations in the DNA of the cell)

To help your immune system to function properly, effectively, and efficiently, healthful behaviors such as eating healthy, getting plenty of rest and exercise, refraining oneself from harmful activities, and having regular checkups are needed.

**Regular checkups** are important because it will be easier for a disease to get treated if the disease is discovered early. More importantly, regular checkups can give an overview of how healthy an individual is, and help him or her to maintain proper health for longer life.

A cancer is caused by several factors such as the mutation in the gene that is responsible for cell growth and division and exposure to radiation and harmful substances. It is not considered an infectious disease since it is not caused by pathogens or foreign cells. Instead, the body is actually harmed by its own cells. However, the gene defect that causes cancer can be inherited from one generation to another.