People's bodies vary in their ability to break down or eliminate certain chemicals due to genetic differences. People may become allergic to a chemical after being exposed. Then they may react to very low levels of the chemical and have different or more serious health effects than nonallergic people exposed to the same amount. People who are allergic to bee venom, for example, have a more serious reaction to a bee sting than people who are not allergic. Factors such as age, illness, diet, alcohol use, pregnancy and medical or nonmedical drug use can also affect a person's sensitivity to a chemical.
Young children are often more sensitive to chemicals for a number of reasons.
Their bodies are still developing and they cannot get rid of some chemicals as well as adults. We don't know all the effects of exposure to every chemical. We learn about the health effects of many chemicals from human exposures and animal studies. Information about human exposures that have occurred at work or by accident is very useful, even though it may be incomplete. For example, if a person has been exposed to more than one substance, it may be hard to find out exactly which substance caused a health effect.