Researchers who found giving mice baths in diluted bleach blocked inflammatory processes that damage skin suggest if the same works in humans, then it could offer a new way to treat skin inflammation from radiotherapy or excessive sun exposure, or even skin damage caused by aging.
The team, from Stanford University School of Medicine, reports the findings in a recent online issue of The Journal of Clinical Investigation.
For decades, baths in 0.005% diluted bleach (sodium hypochlorite) have been used successfully, under expert supervision, to treat some patients with moderate to severe eczema.
For example, in 2009, a team from Northwestern University found that giving children with chronic, severe eczema regular baths of diluted bleach reduced the clinical severity of the condition in cases with secondary bacterial infection.
But until this new study, scientists have not been able to figure out how the bleach baths work.
Antimicrobial effect not the whole story
Lead author Dr. Thomas Leung, an instructor in dermatology at Stanford, has suspected for some time that the antimicrobial effect is not the whole story, as he explains:
"Originally it was thought that bleach may serve an antimicrobial function, killing bacteria and viruses on the skin.
But the concentrations used in clinic are not high enough for this to be the sole reason. So we wondered if there could be something else going on."
Dr. Leung, who is also a pediatric dermatologist at Lucile Packard Children's Hospital, and his colleagues started with the knowledge that many skin conditions, such as eczema and radiation dermatitis, also have an inflammatory component.
Focus on molecule that plays key role in inflammation - NFkB
Inflammation is the result of the immune system sending cells to an injured site to guard against infection. The researchers wondered if bleach somehow intervened in this process to stop inflammation getting out of control.
So they focused on a molecule called NFkB that plays a key role in inflammation, aging and response to radiation. The molecule is a transcription factor, a protein that helps to control gene expression in cells.
When it is not active, NFkB is held in the body of the cell away from the DNA in the nucleus, and when it is activated by signaling molecules, it goes into the nucleus to work on the DNA.
For the first part of the study, the team exposed human skin cells in a test tube to very weak bleach solution for an hour and then treated them with a signaling molecule that activates NFkB so it can enter the nucleus.
They found exposure to the weak bleach solution blocked the expression of two genes that are normally switched on when NFkB is activated. The effect was reversible - 24 hours after the bleach treatment, NFkB was once again able to activate the two genes.
When they investigated further, the team found that the bleach solution blocks the effect of NFkB by oxidizing and disabling the activating signaling molecule. They tested this by making the activating molecule resistant to oxidation - NFkB was able to continue its work unhindered.
Mice responded to daily diluted bleach baths
Researchers found that mice with radiation dermatitis bathed daily in 30-minute bleach solution baths experienced better hair regrowth, healing and younger looking skin.
In the second part of the study, the team looked at how this discovery might be useful in medicine.
They chose to look at radiation dermatitis - an unpleasant side effect of undergoing radiotherapy for cancer that affects the skin in much the same way as a bad sunburn. Sometimes the reaction can be very painful, and the radiotherapy sessions have to stop to give the skin time to heal.
Co-author Susan Knox, associate professor of radiation oncology, says:
"An effective way to prevent and treat radiation dermatitis would be of tremendous benefit to many patients receiving radiation therapy."
For this part of the study, the team gave mice with radiation dermatitis daily 30-minute baths in bleach solution and found they experienced less severe skin damage, better hair regrowth and healing than mice that were just bathed in water.
And finally, because they knew of studies that had linked NFkB with aging, they gave elderly mice dilute bleach baths and found their skin began to look younger:
"It went from old and fragile to thicker, with increased cell proliferation," says Dr. Leung.
And when they stopped giving the elderly mice dilute bleach baths, the effects wore off, suggesting the bathing has to be regular for the skin to keep its thickness.
The team is now thinking about testing the effect of diluted bleach on humans and looking for other diseases that might be treatable. Dr. Leung suggests diabetic ulcers might be one.
Grants from the Dermatology Foundation, the National Institutes of Health and the Howard Hughes Medical Institute helped finance the study.