This seems to explain why I became allergic to the indoor cat I had lived with for 14 years. Red emphasis mine.
http://www.sciencedaily.com/releases/20 ... 083739.htm
"The results of the study are basically of relevance to everyone," says Prof. Maurer. "Especially people who have greater contact with allergenic substances run the risk of developing an allergy some day." They include, for example, people employed in hair salons and in the jewelry and fashion industries, but also hospital staff. "In our research paper we identified the mechanism on which the prevention of an allergy is based," Prof. Maurer explains. The dermatologist and allergist assumes that the results can in future be used in therapy and therefore to avoid allergies.