Most people believe that regular hand-washing is the best way to prevent infections. And they’re right: hand-washing does prevent certain infections, but too much washing can actually help some infections along. What’s going on?

Right now, there are millions of bacteria from hundreds of different species happily residing on your hands, not to mention your teeth, gums, eyes and ears. These bacteria are either transients or residents. Washing your hands helps remove transient bacteria that are just visiting from foreign places like the sink, doorknob and even other people’s hands. Washing shouldn’t remove your hands’ own resident bacteria, though.

While it’s hard to imagine your hands as a bacterial homeland, these residents are perfectly normal and are important in maintaining your health. They help prevent transient bacteria from settling in, and each resident keeps other residents from overpopulating.

If you scrub your skin too frequently, especially with anti-bacterial soap, you could upset resident bacteria, leading to the overpopulation of certain species and local skin infections. Scrubbing away residents might also let transients move in and cause disease. Finally, over washing could break down the skin itself. This allows harmless skin residents to go beneath the skin, where they can become dangerous transients.

So, while a good wash with soap and water is still a great idea, overwashing might lead to some unpleasant symptoms, not to mention inflamed and unsightly hands.