Beyond psychological reactions, the various reactions people have to foods are categorized as true food allergies, food intolerances, food poisonings, and food-borne infections. Hay fever symptoms such as sneezing or asthmatic wheezing may occur. Rarely, migraine headaches can result from an allergy. Symptoms typically occur within 24 hours of eating and may last 1-2 days. Tests for food allergy are not very reliable.
Skin tests are helpful, but result in false reactions two-thirds of the time.
In other words, even though the skin test shows an allergic reaction on the skin, the person can eat the food with no reaction whatsoever. Blood tests may be done, but are similarly difficult to interpret. Remember, most reactions to foods are not allergies. Palpitations from drinking coffee is not caused by allergy. Feeling gassy from milk is not milk allergy.