What are the symptoms of allergy?

Allergies have become an epidemic of the 21st century. Substances that cause allergy reactions are called allergens. 

A symptomatic allergy will exhibit different symptoms depending on the location of the reaction.

Food sensitivity can affect virtually any organ system in the body. In digestive tract, the allergy may cause nausea or vomiting; in the skin, it may cause rashes and in the nasal passages and lungs, it may cause inflammation or asthma.

Because food is ingested into the gastrointestinal tract, GI symptoms should be the first consideration in deciding whether food allergy could be a significant problem.

Gastrointestinal symptoms in food allergy are often chronic or acute vomiting, diarrhea and colic. Colic appears to be a common symptom, but nearly always in combination with other symptoms.

People who have life-threatening reactions usually have asthma and frequently have a history of atopy, including atopic dermatitis and food allergy as young children.

Symptoms may develop within minutes to a few hours after ingestion of the food, and in life-threatening cases, symptoms include sever bronchospasm.

In adults, food allergy triggers most often the oral allergy syndrome, which occurs almost exclusively and an immediate, IgE-mediated reaction.

The short time interval between allergen exposure and onset of symptoms such as itching of the buccal mucosa, and the classical set of food like apples and other pome fruits that triggers the oral allergy syndrome make diagnosis usually easy.
What are the symptoms of allergy?