With chemicals that can harm you, one size does not fit all

When the U.S. Environmental Protection Agency (EPA) evaluates chemical risks, it assumes for the most part that we are all the same. Or, rather, that some of us might be a little bit more sensitive than others. Ten times more sensitive, to be specific. But that’s not exactly true. When it comes to chemicals in the environment that can harm you, one size does not fit all.

How chemical exposures can impact our health

Chemicals can impact our health in a variety of ways – they can lower our immune systems, increase our blood pressure, change the way we think and the way our brains develop, impact our ability to have healthy pregnancies, and affect our health as we age. But are we all affected in the same way? Definitely not.

Some people are much more sensitive than others. But how EPA currently conducts risk assessment (for health effects other than cancer; for cancer they don’t even do the bare minimum) is by assuming that the most sensitive among us are 10 times more sensitive than the average healthy person, using what’s known as an adjustment factor. But scientists know that the range of how we respond to chemical exposures can be much greater than that.

As outlined in our recent review paper, Current practice and recommendations for advancing how human variability and susceptibility are considered in chemical risk assessment, data show that some people are more than 10 times more sensitive than their counterparts.

For example, the Office of Environmental Health Hazard Assessment in California (OEHHA) accommodates the fact that children and young infants are more sensitive to air pollution by using a factor of 30 (rather than 10) based on how young people metabolize chemicals compared to adults. Indeed, we are more sensitive to chemicals, such as those that can mess with our hormone signaling (called endocrine disrupting chemicals) during critical stages of development, such as fetal development, in early life, puberty, pregnancy, and as we age.

So, what else can make one person more sensitive to chemical exposures than another? 

Why we respond differently to chemical exposures

There are many things that can increase our sensitivity to the chemicals we are exposed to, including the amount and how often we are exposed to said chemical, what our underlying heath status is (our genetic make-up, whether we have any pre-existing conditions, where we live and work (if we are exposed to additional sources of pollution), and whether we experience social stressors like racism, poverty, or hunger and that we are already exposed to many chemicals. 

A solution that includes all of us

Just like pre-existing health conditions and other factors can make us more susceptible to a virus, they can also make us more susceptible to the harmful effects of chemical exposures. And while the EPA assumes we are all relatively similar when it evaluates our risks regarding chemicals in the environment, it’s often our differences that set us apart and determine who is most at risk.

Therefore, we call on the EPA to acknowledge our differences by considering the full range of human variability and susceptibility in chemical risk assessment. This important step forward by the EPA would get us closer to the goal of risk assessment, which is to protect the entire human population, including those who are the most at-risk.


This post is third in a series about our Roadmap papers, which provide scientific recommendations to update chemical risk assessment to better reflect exposures and hazards, guide decision-making, and protect the public’s health. Lead authors of the papers will discuss their recommendations on a webinar on Thursday, February 2nd. Register here: bit.ly/san-jan23

Other blogs in this series:


About the Author

Julia Varshavsky, PhD is a professor of health sciences at Northeastern University in Boston, MA, and an environmental heath scientist and environmental epidemiologist who cares about protecting the public from environmental chemical exposures.