Allergic reaction can happen when the allergen enters the body either by swallowing, breathing or touching it. Common allergens include foods (e.g. peanuts), drugs (particularly antibiotics such as penicillin), dust and venoms from the stings of insects (e.g. bee, wasp, yellow jacket, hornet, fire ant). Generally, any kinds of allergen have the potential to cause urticaria. Even latex can be an allergen to some people.
If an allergen causes urticaria or swelling, it usually enters the body through the mouth (e.g. food, pills) or through injection (e.g. medicine, insect stings).
