The effect of perfume "ageing" on the allergenicity of individual perfume ingredients.
An ingredient of a perfume which is a sensitizer may become hypoallergenic by interacting with other ingredients during the ageing process of the perfume. Thus, a patient with an exquisite allergic sensitivity to cinnamic aldehyde tolerates two perfumes containing cinnamic aldehyde without acquiring a dermatitis. There are several theories of why cinnamic aldehyde can become a non-sensitizer in a perfume mixture. Testing with a mature perfume may be much more significant than testing with individual ingredients.