Common antibacterial also suppresses mast cells--maybe why it works for eczema

Triclosan is a well-known antibacterial found in soaps. I know I've seen it listed on every pump-container of liquid soap that claims to "kill 99% of bacteria," whatever that means. (99% of species? 99% of one species?) What I didn't know until recently about triclosan, which is found in a wide range of consumer products, is that it relieves symptoms of eczema. But scientists are not sure exactly how it works.

New research by scientists led by Julie Gosse at the University of Maine shows that at least one reason that triclosan helps reduce eczema symptoms is that it prevents mast cells in the skin from releasing histamine and other allergy-mediating molecules. Triclosan prevented the scientists' model cells from getting activated in general. In short, it's an immunosuppressant.

Mast cells have molecules on their surfaces that bind to IgE antibodies--the type responsible for allergic hypersensitivity. When mast cells encounter antigen, perhaps from food or pet dander, they release histamine and other molecules, which cause inflammation.

The scientists, working with a laboratory cell line that they claim is identical to mast cells, found that doses of triclosan significantly reduced the amount of one molecule, beta-hexosaminidase, released by the cells when they met antigen.

Activated mast cells change shape, ruffling around the edges. Triclosan also prevented this from happening.

The scientists claim their results show that reducing "degranulation"--the release of granules stored by mast cells--is the way that triclosan helps alleviate skin inflammation in eczema.

Through the paper, the authors refer to histamine--but reducing histamine probably isn't the main avenue by which triclosan acts. If you have eczema, you know that antihistamines don't help. I don't know why some doctors prescribe them. Relatively recent research (I wrote about it here) has identified a neural itch pathway independent of histamine.

So what good is this research?

It helps clarify the picture of what triclosan is doing. It's a contribution that could, in the end, help produce another topical anti-itch ointment that incorporates triclosan or some derivative, possibly together with a steroid. You'd think it'd be a no-brainer, because of its antibacterial properties. But, like any drug, triclosan comes with its own side effects.

[Edited Jan.13]