Two new pieces of research suggest they may be.
Children are less likely to become sensitive to allergens if they have a dog in the home, according to German scientists, while an American study found that regular social interaction reduced children's risk of leukaemia by about 30%.
These findings seem to chime with popular perceptions of "cotton wool kids" and the belief that our increasingly sterile, urban and risk-averse society paradoxically creates new dangers for our children.
The causes of leukaemia are complex, and most childhood leukaemias begin with a genetic mutation, so the US study is far from conclusive. But there's an established hypothesis that if an immune system is not challenged early (our immune responses develop from birth to about age 12), it can increase the risk of developing allergies and illnesses.
Ken Jones, professor of immunology and allergy at the Cardiff School of Health Sciences, explains that our immune response has taken millions of years to develop, so rapid changes - notably, the proliferation of allergies - cannot be genetic.
Source - Guardian