The immune system is only trying to help, of course. When we get cut a cut or wound, immune cells rush to the area to fend off foreign particles that might cause infection. And some inflammation is inevitable. But too much inflammation is bad–it can cause diseases like rheumatoid arthritis. So according to the study, skin bacteria dampen the immune cells’ activity enough to prevent excessive inflammation without hampering the immune system’s ability to fight infection. This doesn’t prove the hygiene hypothesis, exactly. But it does show that bacteria on, and maybe in, our bodies help the immune system do its job without going out of control.