How do i know i'm allergic to dairy?

Sx : Allergic reactions usually occur from minutes to 2 hours after ingestion of dairy. The symptoms may be flushing, itching, hives, nasal congestion, abdominal upset or even asthma. In severe cases, death may result. This must be distinguished from the gastrointestinal symptoms when one is lactose intolerant . Positive skin test or blood test is helpful,but oral challenge is the gold standard.