The most common reaction is referred to as allergic rhinitis, with the usual accompanying respiratory discomfort, and is caused by inhaling allergens. Asthma is a much more serious disease, and results in wheezing and shortness of breath due to a narrowing of the bronchial tubes. Asthma is caused by sensitivity to certain allergens and may be irritated or aggravated by respiratory tract infections. Skin allergies usually occur after contact with an allergen. They include eczema or atopic dermatitis and are marked by itchy rashes, and oozing blisters.
Hives involve swelling, redness and itching.
Allergies to certain foods, such as fish, eggs, milk, nuts and wheat induce intestinal disturbances and occur in children who usually outgrow it after age three. Anaphylactic shock is the most severe of all allergic reactions. Vomiting, cramps, and a sudden drop in blood pressure can also result. Anaphylaxis often occurs in persons particularly sensitive to penicillin, stinging insects and shellfish or nuts. Many people have difficulty differentiating between a cold and an allergic attack.