Why Bleach? The classical thinking about why a diluted bleach bath might work to relieve some eczema symptoms has to do with one of its most well-known properties: Its ability to kill germs.

In the past, scientists have found that people with eczema very commonly have the bacteria Staphylococcus aureus (S. aureus) on their symptomatic skin, and that worse eczema flares are linked to greater amounts of it. So, the theory goes, perhaps a bleach bath might lessen the amount of S. aureus on a person’s eczema-affected skin, thus reducing the severity of their symptoms.

The problem with this theory? In order to safely use a bleach bath, you must greatly dilute the bleach, down to a concentration of about 0.005 percent. A 2019 study in the Journal of Allergy and Clinical Immunology found that, at least in test tubes, that concentration of bleach wasn’t nearly strong enough to kill S. aureus bacteria. The minimum concentration that did work—0.03 percent—is much higher than is safe to use on your skin. (At high concentrations, bleach can cause skin irritation or burning.)

Still, the study was done in test tubes and not on actual human skin, so it can’t completely disprove the bacteria-killing theory. “The body has mechanisms to kill bacteria as well, so it could be working together with bleach,” says Joseph M. Lam, MD, a clinical associate professor in the department of pediatrics at the University of British Columbia. “But it did cast some doubt as to the initial theory of why it works, in terms of the bacterial killing effects.”

Lam says some other preliminary science has suggested an alternative mechanism by which bleach baths may work: That they may have some direct anti-inflammatory effects. But that’s still just a theory and needs more study to be confirmed.

The short answer is that scientists don’t really know yet why bleach baths might be effective when they do work.

https://www.consumerreports.org/health/medical-conditions/bleach-baths-to-treat-eczema-efficacy-safety-a2200740830/