Q. Is there any validity to the popular claim that one can “sweat out toxins?” If so, what “toxins” can the body sweat out?

A. The body does appear to sweat out toxic materials — heavy metals and bisphenol A (BPA), a chemical found in plastics, for instance, have been detected in sweat. But there’s no evidence that sweating out such toxins improves health.

“The claims for the benefits of saunas and other sweat-inducing treatments are not backed by science,” said Dr. Harriet Hall, a retired family physician and former Air Force flight surgeon, who edits the website Science-Based Medicine and is a co-author of “Consumer Health: A Guide to Intelligent Decisions.”

The concentration of metals detected in sweat are extremely low. Sweat is 99 percent water. The liver and kidneys remove far more toxins than sweat glands.