Found this on Dr Art Ayers Cooling Inflammation blog in his response comments to one of his readers.
Probiotics are a quick fix for about 10% of the lacking bacterial species. Most of the lacking bacteria must be acquired by eating fresh vegetables with clinging live bacteria. Many bacteria are also recruited for the gut from contact with people and animals. Thus, hand washing is OK for decreasing exposure to flu viruses, but it also stops the spread of healthy bacteria needed for normal immune system development.
Cleanliness is next to sickliness. Start composting and have your whole family get involved in gardening and mud fights. You also would benefit from having a dog that spends time digging up bones. Kissing is also very healthy.
Maybe our ancestors rarely got sick in the caves. Maybe washing up in the local stream or nearby lake/ocean was sufficient.
Are we too clean?
Update: Have a look at the newest article in the link below from Dr Ayers. While I understand that being "metro" clean could be excessive, I'm not sure I'm ready to buy into the idea that it's healthy to just cruise around in life with filthy hands. But he reiterates again his points about how eating certain foods can cure lactose intolerance because of the new bacteria that can digest the lactose. Some people on PaleoHacks strongly contested this based upon their own personal experience, but I doubt that Dr Dyers is just typing this stuff up for kicks and giggles. I'm certainly not arguing with anyone's personal experience. How can I? But has anyone successfully become lactose tolerant after being intolerant?