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In a study of adults with atopic dermatitis (AD), twice-weekly bleach baths led to significant improvements in itching, disease severity, and skin barrier function. Bleach baths' exact mechanism of action, however, remains unclear.

The study results appeared in the .

The non-randomized, open-label trial included 15 adults with AD who tested positive for Staphylococcus aureus bacteria on the skin surface, as well as five healthy controls who were negative for the bacteria. Both groups were instructed to take two bleach baths each week for 12 weeks. At the trial's conclusion, eight (53.3%) patients experienced improvements in Eczema Area and Severity Index (EASI) scores and significant reductions in itch, while 87% reported improvement in sleep and measures of skin barrier function.

At the same time, bleach baths had no significant effect on S. aureus culture-positivity or abundance, leaving scientists to continue hypothesizing on how bleach baths achieve these effects.

Lisa Beck, MD, a dermatologist-researcher and principal investigator in the Atopic Dermatitis Research Network at the University of Rochester Medical Center in New York state, served as the study's senior author. Beck recently discussed the study and its findings with the Reading Room. The exchange has been edited for length and clarity.

How would you encapsulate the impetus for this investigation?

Beck: In 2009 a pediatric study highlighted that bleach baths led to clinical improvements in infants who tested positive for S. aureus. But, to the researchers' surprise, the children remained S. aureus culture-positive.

That led to a flurry of different trials, most of which found clinical improvement while noting that bleach baths did not seem to reduce S. aureus.

We wanted to take a look at bleach baths again, focusing on adults. We developed this open-label, non-randomized trial, where we brought in adults with mild-to-severe AD and compared them with non-atopic healthy controls. We provided the bleach and gave them the cup measurement. We assessed what happened to the abundance of S. aureus, what happened to barrier function, and what happened to itch.

Would you describe your key findings?

Beck: Bleach baths had no significant effect on S. aureus culture-positivity, absolute abundance, or microbial diversity. However, this isn't that surprising, because it takes more than a tenfold higher concentration of bleach to kill S. aureus in a test tube than what is used in a bleach bath. At that higher dose, unfortunately bleach would also cause epithelial death. So we weren't even at the right concentration to kill S. aureus and we probably should have known that.

This study also demonstrated that bleach baths provide similar improvements in adults as had been seen in kids.

We also saw improvement in itch. I think we were the first to specifically show improvement in this key AD symptom as a function of bleach bath treatments in eczema patients.

How might bleach achieve these improvements if it is not impacting S. aureus?

Beck: It might actually be that bleach is a bit irritating to the skin, but for some reason it's an irritation that initiates a beneficial immune response. And that response includes repairing the skin barrier defect commonly seen in patients with AD.

Earlier studies had demonstrated that bleach, at about the concentration used in these bath treatments, can inhibit inflammation by regulating the transcription factor known as nuclear factor-kB (NF-kB). This reduction in skin inflammation may be responsible for both reductions in itch, improvement in barrier function, and, ultimately, clinical improvement.

Based on these findings, what are your suggestions for dermatologists who treat adults with AD?

Beck: This is a therapy worth considering for people of any age for whom itch is a big problem, and it is particularly helpful to employ at nighttime.

Bleach baths are most effective for those who have a bathtub. We have worked out squirt bottle options but we don't think they are quite as effective.

The specific advice is to use a quarter-cup of bleach in a standard adult bath twice a week, and spend about 10 minutes in the bathtub. Patients should use a washcloth to get the water everywhere there is eczema -- don't just let it be from the waist down because that would then be the only place that would get better.

The AD treatment landscape is rapidly changing, with a number of new targeted biologics and more general anti-inflammatory approaches that are becoming more widely used. But I try to remember to discuss bleach baths with many of my patients. I think it is valuable to remember something so cheap, accessible, and relatively easy to incorporate into a patient's treatment plan, be it as a monotherapy or add-on therapy. Bleach baths can result in a notable improvement in several key features of their disease.