Toxicology basics · Concept 9 of 9 · 3 min

Groups and individuals

Limits keep risk low for groups, with room for the people who react more. Your own case depends on where you sit.

A limit protects a group; a decision is about you (my example).

The idea

People differ in how much they're exposed and in how they respond, for example through asthma or genes US EPA, 2026. Limits are set to cover sensitive groups, not only the average person US EPA, 2026. One of the usual factors of 10 is there for differences between people US EPA, 2026. Exposure checks also look at the high end, around the 90th percentile, not only the middle US EPA, 2026. Where you sit in the group, more exposed or more sensitive, is the part only you can add (my example).

Groups and individualsA hump showing how many people respond at each strength, from less sensitive on the left to more sensitive on the right. The right tail is shaded. A dashed line marks the limit, set to cover the sensitive end, not just the average.average personlimit covers hereless sensitivemore sensitivePeople in a group
A spread of people from less to more sensitive, with the limit set to cover the sensitive end (my example).

Use it on a case

To place yourself:

  1. Are you more exposed than most, through your job, hobbies or where you live?
  2. Do you have a condition, like asthma, that makes you react more?
  3. Start from the group numbers, then adjust for those two answers.
  4. For a health decision, a doctor who knows you can do this placing with you.

An example

Two neighbors get the same radon result (my example). One works from home in a basement room; the other is out most of the day (my example). Same test, different exposure, and a different sense of how fast to fix it (my example).

What it can't tell you

Group numbers can't say how one person will fare; they say how a group like them did (my example).

Connects to

Sources for this page

  • US Environmental Protection Agency (2026). Conducting a human health risk assessment.

    Health agency advice: what a public health body recommends; check the page for its own sources.

    What we use: How agencies go from dose to limit: the NOAEL is the highest tested dose with no meaningful increase in harm; the LOAEL is the lowest dose that showed one. A daily reference dose is the NOAEL divided by uncertainty factors, usually 10 for animal-to-human and 10 for differences between people (100 together). Effects with a threshold get a curve that is flat at low doses; for cancer, a straight line from zero is the default when the mechanism isn't known, and its slope gives the extra lifetime chance. Durations: acute (hours to a day), subchronic (weeks or months), chronic (a large part of a lifetime; for people, at least seven years). Limits aim to cover sensitive groups (for example asthma or genetics) and high-end exposure, around the 90th percentile.

    Checked Oct 13, 2026 · https://www.epa.gov/risk/conducting-human-health-risk-assessment

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