Allergies are exaggerated immune responses to environmental triggers known as allergens. Allergies are very common, and about 50 million people in North America suffer from allergies. One of the most common forms of allergy is allergic rhinitis ("hay fever"), which produces symptoms like
The symptoms of hay fever can, in turn, lead to fatigue and lethargy. Other types of allergic reactions can involve the skin (hives and itching). Anaphylactic shock is a severe form of allergic reaction that can be life-threatening. In anaphylactic shock, there is swelling of the throat and difficulty breathing. Asthma is also related to allergies in many cases.
The symptoms of allergies can sometimes resemble those of other conditions. The common cold and the flu can cause respiratory symptoms similar to allergies. Typically, allergy symptoms are associated with a specific time of year or exposure to an allergen.Summary of Common Allergy Symptoms by MedicineNet Staff