An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.
The site is secure.
Thehttps:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.
National Institute of Environmental Health Sciences
Use this QR code to view the newest version of this document
Your Environment. Your Health.
Last Reviewed: December 22, 2025