Researchers from the School of Medicine at the University of California have shown that the more germs a child is exposed to, the better their immune system in later life. Their study found that keeping a child's skin too clean impaired the skin's ability to heal itself. From the article: "'These germs are actually good for us,' said Professor Richard Gallo, who led the research. Common bacterial species, known as staphylococci, which can cause inflammation when under the skin, are 'good bacteria' when on the surface, where they can reduce inflammation."