The nature and extent of an allergic reaction differs from person to person, and also depending on which type of allergen is involved. Ambient allergens such as pollen and dust are airborne particles. It follows then that a reaction will typically occur in the areas of the body that are in contact with the air, such as your nose, eyes, and lungs. Examples are hay fever, or allergic rhinitis, with symptoms including sneezing, itching and red eyes. If the airborne particles are inhaled, there will be an increase in mucous production in the lungs, leading to coughing, wheezing and shortness of breath.
Non-ambient allergens include those found in food, insect bites and medication. Food-allergy symptoms include bloating, vomiting, diarrhoea and abdominal pain, but can also affect the skin in the form of itching and hives. Food allergies seldom cause respiratory reactions or rhinitis though. The symptoms of insect-bite allergies include reactions in the digestive tract such as vomiting and diarrhoea; reactions on the skin such as swelling; and respiratory reactions such as finding it hard to breathe. The symptoms of a medication allergy are sometimes confused with the medicine’s side effects. Real drug-allergy symptoms can be life-threatening.
Reactions to insect stings, antibiotics and medications and even certain foods can be severe and include anaphylaxis. This is a whole-body reaction where multiple organ systems are affected, including the digestive, respiratory and circulatory systems. Anaphylaxis can be fatal and signs of it include broncho-constriction, skin reactions, swelling, low blood pressure, and coma. The onset can be immediate or delayed, and the symptoms may recur after subsiding.