Allergology is also a "modern specialty"; the frequency and gravity of allergies are increasing. Allergology is hereditary on the one hand, and related to the environment on the other hand.
As far as the hereditary aspect is concerned, an allergologist will not simply treat Mr or Mrs Smith but rather their entire family.
As far as the environment is concerned, numerous allergens (both old and new) cause allergies. Allergies are generally diagnosed through interviews, skins tests and blood samples.