I was just thinking this today as I tapped my ds' back as he vomitted into a bucket.
When ds was first born I was hyper vigilant/clean/anti-bacterial. everything was always sterilised, anti-bacterialised. His face/hands were always wiped clean. he was bathed every single day. Anytime his clothes got a speck of dirt on they were changed (a whole heap of washing). Floor was hoovered 5 times a day, not allowed to eat of anybody else's plate or use cutlery if it hadn't been at least boiled. If I caught him eating another child's apple or drinking from their cup I was over there in a second to take it off him. Vitamin drops every day etc. etc.
Fast forward two years to dd's arrival, by now I'd gone almost completely in the other direction, mostly because I didn't have the time, I was knackered I was back working after 2 weeks (cm). Nothing got sterilised (just washed with everything else), hands and face always grubby. Bathed twice a week or so. Clothes changed once or twice a day (day clothes/night clotes) unless vomitted on or soiled. Floor hoovered once or twice a day if that. If she ate some body elses anything unless they were upset I left her too it.
The difference in both of the children are remarkable. Truly. Ds has eczema/asthma and catches almost every bug. DD, never really has anything. Rarely even a cough. The only major things she has had were chickenpox and hand and mouth. Ds has the vomitting and diaorrhea (spelling) bug at least once a year and coughs every couple of months. Dd hasn't had it once.
I also b/fed dd 2 months longer putting her straight onto cows milk whereas ds stopped at 8 months and went on to formula.
AIBU thinking that living in a sterilised environment produces children with a lower immunity or are my dc's an odd case.