The following is from http://blog.petspyjamas.com/getty-dog-owners-vs-cat-owners-unbelievable-facts/9/:
9. Cat owners have a lower chance of developing allergies
When cats enthusiastically rub themselves against your legs, it isn’t just out of affection or a desire for food. Those clever cats are also helping to boost your immune system, and are particularly great for triggering allergy immunity in babies. No wonder they were worshipped as gods in ancient Egypt!
Is it true?
The evidence is somewhat mixed. Maybe. In summary, there is conflicting evidence. None of the evidence here is particularly strong. I conclude that cat exposure is neither associated with a strong benefits nor detriments, or we might expect to see more consistent results.
None of these studies are sufficient to show causality - merely suggestive correlation.
This was only a survey but it found cat exposure was negatively correlated to allergies.
Children exposed to pets during the first year of life had a lower frequency of allergic rhinitis at 7–9 years of age and of asthma at 12–13 years. Children exposed to cat during the first year of life were less often SPT positive to cat at 12–13 years.
Exposure to animal dander did not influence the prevalence of clinical disorder, but positive SPT reaction to cat dander was more prevalent in infants who were exposed to cats and/or dogs (p = 0.04)
So cat exposure isn't associated with serious allergy problems, but is associated with subclinical ones.
This was a study focussed on cow's milk, but as an aside:
Allergic disease was not associated with exposure to tobacco smoke, house dust mite antigen, or cats.
So cat exposure is UNcorrelated with allergies.
However, no relation between early indoor allergen exposure and the prevalence of asthma, wheeze, and bronchial hyper-responsiveness was seen.
So, cat exposure is UNcorrelated with allergies.
