Anaphylactic reactions are usually characterized by their sudden onset and dramatic presentation which may at times be life threatening. Symptoms may associate a sudden drop in blood pressure with potential loss of consciousness or mental confusion, rapid heart rate and usually general flushing. Other systemic symptoms may also be present such as generalized hives and swelling (urticaria and angioedema), acute shortness of breath with obvious and wheezing. Systemic reactions are more common than true anaphylactic reactions with loss of consciousness.

Anaphylactic reactions are mostly due to immediate reactions which can be triggered by foods, insect stings (bee, wasp, etc), drugs (penicillin and others), exercise or may occur without a known trigger. Patients must be evaluated for identification of the potential trigger and treated accordingly. They must be correctly educated and supplied with epinephrine and antihistamines to be used during potential future reactions.