Why allergic dermatitis recurs

Allergic dermatitis is particularly easy to relapse, because most allergic dermatitis, allergic reasons are not clear, did not find. If caused by hair dye, no longer dye is not allergic, but there are many unknown factors, such as biological factors, environmental factors, it is invisible, fungal spores only visible under the microscope, there are dust, mites, etc., allergic constitution, contact allergens on the crime, so the reason is not removed, this allergic dermatitis on the old recurrence.