Yes I think than being exposed to germs etc, help your body build up immunity to lots of things ,, As kids in the 1930's we were exposed to lots of things , Childhood illnesses like mumps, measles, chicken pox were usual and most kids got them .. Scarlet fever and diphtheria were the ones to be avoided .. Lots of things done then that would be taboo today ,, food in open sacks , things like flour, rice, dried vegetables , porridge oats served with a scoop into paper bags . but the flies would be all around them .. Also big blocks of sticky dates that were out in front of greengrocers , cut lumps off with a knife for customers,, again flies all over the block .. .. Meat hung up outside the butchers shop on rails again flies , dust etc ,, but we didn't seem to come to any harm .. All this sterility seems to breed a fragile race of people who succumb to everything going ,, Also re swine flu now prevalent ,, mainly younger people who get it ,,, The older ones seem to have some resistance created by viruses they have run into many years ago ,,