Consider the effects of health hazards as one approach to assess them. A risk factor is defined as an activity or circumstance that enhances the likelihood of sickness or harm. You have no control over the health hazards that are inherited. The physical and social circumstances that surround a person are referred to as their environment. These include their life style, occupation, and community background. All these factors can affect a person's chance of getting sick, dying early, or suffering from injury. The health risks associated with exposure to chemicals depend on how you measure them. There are two main ways of evaluating health risks: hazard analysis and critical effect studies. In hazard analysis, scientists estimate what might happen in real life if someone is exposed to a certain amount of a chemical. They then compare this possible outcome to what happens without the exposure. If the possibility of something bad happening is high even when there is no actual exposure, then they know that the substance is harmful. In critical effect studies, researchers test what actually does happen in real life if people are exposed to different levels of a substance. They look at the number of cases of disease, birth defects, miscarriages, and other problems in those groups. From this information, they can say with some certainty how much exposure is too much and what effects that level of exposure has on people.