How to tell if I have an allergic reaction to dairy?

Timing and symptoms. Dairy or milk allergy is most common in young children and can present as hives, rash, cough, vomiting, diarrhea, flare of eczema or even more severe symptoms. The symptoms will improve when dairy is stopped and return if dairy is reintroduced. An allergist can perform a skin test or order a blood test to confirm your suspicion.