the idea the exposure to dirt, of all sorts, makes for a strong healthy imuno system has been called the hygene factor.. if as child, you don't get to eat a pound of dirt you won't be healthy. (old wife's tale is a child will eat a pound of dirt before they grow up, so mothers don't have to fuss to much about dirty fingers all the time, even if they generaly do) there seems to be some truth to the old wifes tale.
children who are keep very clean, and who are treated with antibotics at the first exposure to a pathogien, end up with imunosystems that are hyper active.. and start acting up-- alergies are the syptom.
(i call it the cockroach factor-- cockroaches have been around since the dinosuars.. they are always found in places with poor hygene, damp, fetid arears. there must be something about poor hygene that is actually good for you. very tellingly, my son, with whom i made an attempt to keep things very clean, has alergies.. his younger sister has none.)
