Reference summary — not medical advice or a personal risk estimate.
Ionizing radiation (X-rays and gamma rays)
Quick answer
Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Whole-body radiation. Medical imaging (CT scans, X-rays, certain treatments), some occupations (radiology, nuclear industry, flight crew), and rare environmental sources.
Summary
High-energy radiation from medical imaging, nuclear sources, and some occupations is associated with increased cancer risk.
Detail
X- and gamma-radiation are Group 1 with sufficient evidence for many cancers including leukemia, thyroid, breast, lung, stomach and others. The added risk from a single low-dose medical procedure is generally small; cumulative lifetime exposure matters. Clinical decisions about imaging are between a patient and their care team.
What's not established
This classification is based on sufficient evidence in humans that this factor can cause cancer. It does not establish a safe exposure threshold, your personal risk, or how this factor's risk compares in size to other Group 1 agents — hazard classifications are not ranked by magnitude.
Regional relevance
global
Documented in these products
Presence in a product category doesn't imply the product causes cancer. Click each to see the source and context.
Evidence sources
Every claim on this page traces back to one of these. Click through to read the primary document yourself.
Primary sources
IARC
IARC Monographs — Classifications by Cancer Site, Vols 1–140
NCI
NCI — Risk Factors: Radiation
Supporting sources
ACS
ACS — Known and Probable Human Carcinogens
Cancer Research UK
Cancer Research UK — Causes of cancer and reducing your risk
IARC / WHO — European Code Against Cancer
European Code Against Cancer (5th edition) — 14 ways you can help prevent cancer
NTP
NTP — Report on Carcinogens (US National Toxicology Program)
Last reviewed: October 2026
Official reference list
A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.
- California Prop 65 list
State of California's list of chemicals known to cause cancer or reproductive harm.