Flea allergies will go away if the source is removed and no more flea exposure occurs. (vetlive.com)
A diagnosis of FAD may be determined after assessing the history (age of onset, duration and seasonality of signs, known or suspected environmental flea exposure) and physical examination findings (pruritus, compatible clinical signs, and lesion type and distribution pattern). (todaysveterinarynurse.com)
The exact amount of flea exposure required to trigger an allergic reaction likely varies between individual animals, but we know that it does not take a heavy flea burden to elicit signs of FAD. (adavet.com)