According to BBC News, recent research supports the hygiene hypothesis:
Normal bacteria living on the skin trigger a pathway that helps prevent inflammation when we get hurt, the US team discovered. The bugs dampen down overactive immune responses that can cause cuts and grazes to swell, they say.
And other recent research says it’s wrong:
The decades-old “hygiene hypothesis” holds that early exposure to microbes somehow challenges the immune system and strengthens it against allergies. Studies have shown children exposed to bugs by older siblings or attending nursery cut their future allergy risk.
But new work published by the American Thoracic Society casts doubt on this.
The study by Dutch investigators at the Erasmus University found although children in day care got more colds and other infections, they were just as likely as other children to go on to develop asthma or another allergy by the age of eight. The children who went to nursery and who had older siblings had more than quadruple the risk of frequent chest infections and double the risk of wheezing in early life, with no obvious pay off in terms of later protection from allergy.
The original hygiene hypothesis said that exposure to harmful germs (e.g., that cause colds) cuts down on allergy risk. But it’s now clear it’s the exposure to harmless germs (e.g., in dirt) that’s helpful.
Allergies in the UK have tripled in the last 10 years. I believe this is due to greater consumption of food that is germ-free, such as factory food and restaurant food. Shelf-life considerations and food-safety laws, in other words.
Advice given by Allergy UK:
The best advice we can currently give to parents is not to smoke around their children and make sure they have a balanced diet and get plenty of exercise.
Not even close to what I think. My advice is: Feed your kids plenty of fermented food, such as yogurt. I’d bet a lot of money that my advice is better.
Thanks to Mark Griffith.