Hormesis

Hormesis is a biological phenomenon by which a beneficial effect is recorded as a result of something that is ordinarily considered toxic. Simply put, in some cases it can be more harmful to not be exposed to any toxicity than to a small dose.

Examples of hormesis
Many common substances and can be harmful in large amounts, but are beneficial in smaller dosages. This includes salt, UV-rays in sunlight, and dioxin (a well-known environmental toxin), as well as other activities that subject the body to biological, chemical or physical stress, such as calorie restriction, cold temperatures, heat shock and hypergravity.

Interestingly, the same phenomenon has been present in people exposed to radiation, such as radon. Though its radiation is considered ionizing and detrimental, often linked to an increased risk of cancer, studies show that people exposed to low radon levels are less likely to develop cancer than those exposed to none at all. They document reduced rates of cancer and death for in certain demographics with a higher general exposure to radiation, such as industrial workers who handle low-level radioactive materials, residents of high altitude regions, people exposed to higher levels of natural radon gas and survivors of atomic blasts who lived outside of the immediate blast areas.