Interesting medical college article, especially if you suffer from an autoimmune disease. Click here. If this hypothesis is true, a little dirt and germs as a child could be beneficial.
"Increased hygiene and a lack of exposure to various microorganisms may be affecting the immune systems of many populations - particularly in highly developed countries like the US - to the degree that individuals are losing their bodily ability to fight off certain diseases.
That's the essence of the 'hygiene hypothesis', a fairly new school of thought that argues that rising incidence of asthma, inflammatory bowel disease, multiple sclerosis and perhaps several other diseases may be, at least in part, the result of lifestyle and environmental changes that have made us too 'clean' for our own good."