Americans have been on an antibacterial kick for the past several years. Our hand soap, dish soap, and body wash have morphed into an arsenal of bug-killing napalm, eliminating all but the heartiest of bacteria.

And there are, indeed, some scary microbes crawling around out there—Staph and C. Diff, just to name a couple. But scientists are in the midst of discovering that not all bacteria are bad. In fact, the vast microcosm of life—bacterial, viral and fungal—that lives in and on us is not only mostly harmless but is actually necessary for our own good health.

Recent research has revealed that when we wipe out certain beneficial bacteria in our guts (with, say, a round of antibiotics prescribed to kill off a harmful bug), other, unwelcome species of bacteria can then move in and cause health problems.

A new study finds that the same might well be true for our skin. No matter how many showers you take each day, you're still a walking colony of bacteria. And that's a good thing, suggests research published online July 25 in Science.

A team of researchers led by Shruti Naik, of the National Institute of Allergy and Infectious Disease's Laboratory of Parasitic Diseases, examined what happens when mice were raised without the standard communities of skin microbes. One of the common, commensal bacteria is Staphlococcus epidermis. Without this friendly population on their skin, mice were more likely to get infected by the parasite Leishmania major (one species of Leishmania, which can cause leishmaniasis in humans, resulting in boils and open sores that do not heal).

The reason goes beyond a simple issue of clearing space for the invading bacteria to move in. Instead, the researchers suggest, the reason for worse infection hinges on interleukin 1 (IL-1) signaling, an immune response that the helpful bacteria can influence. "Resident commensals are required for optimal IL-1 signaling in the skin," Naik and colleagues wrote. And that means that they, in turn, "are necessary for optimal skin immune fitness." Past studies have implicated IL-1 signaling in psoriasis as well as asthma and arthritis.

The researchers also tested gut microbiota's effects on skin infections. Even though they live inside the body, gut flora indirectly help the skin fight off infections by contributing to immune system development and regulating some inflammatory responses. But they found that gut bacteria were much less important than skin bacteria to the development of the skin's immune response.

These findings suggest that our much-ignored commensal skin bacteria play an important role in fending off infections. So perhaps all of those antibacterial baths are having effects that are more than skin deep.