The common allergic reactions and diseases are :
- allergic asthma
- allergic rhinitis (hay fever, perennial rhinitis)
- urticaria (hives)
- allergic contact dermatitis
- food allergies
- drug allergy
Allergic rhinitis is a common chronic disease characterized by repeated attacks of itching of the nose, runny nose and sneezing. It is often associated with allergic conjunctivitis – watering, itching and redness of eyes. Allergic rhinitis develops due to allergic reactions to allergens in the air (like pollen) that can get attached to the mucosa of nose and the conjunctiva.
The seasonal allergic rhinitis (also called hay fever) results from an allergy to seasonal pollen while perennial allergic rhinitis is believed to result from sensitivity to house mite dust or other allergens present throughout the year.
Allergic asthma or allergic asthmatic bronchitis usually presents with a cough or breathlessness and wheezing (abnormal breathing sounds). Allergic asthma occurs from exposure to air-borne allergens. Inhalation of these allergens stimulate immune reactions which results in constriction of the bronchi, and increased mucus secretion. Iti s often associated with allergic rhinitis or other allergic disorders.
Exposure to cold, smoke, dust, pollen, animal products (hair, scales) and pollen can precipitate the attack or worsen the symptoms.
Anaphylaxis is a potentially fatal medical emergency resulting from an acute allergic reaction (type I allergic reaction). It is characterized by prominent symptoms of various systems – respiratory (breathlessness and wheeze), cardiovascular (low blood pressure) and skin (like itching, flushing).
Anaphylaxis can result from an allergy to certain food items (like egg, milk, sea food), drugs (like penicillin, lidocaine), and insect bites. It usually manifests within a few minutes to a couple of hours after exposure to the allergen.
Urticaria (hives) patients have a severely itchy skin with red lesions that can appear anywhere on the body and be of various sizes. The skin lesions usually last for few hours. Many patients with urticaria may also have angioedema.
Angioedema is the sudden development swelling of the skin, subcutaneous tissue, mucosa and submucosa due to an allergic reaction. It commonly affects the face, hands, feet, and also the genitals. Angioedema (like laryngeal edema) can be sometimes serious enough to cause obstruction of the airway making it a medical emergency.
Angioedema can be caused by a variety of reasons. The angioedema resulting from allergic reactions are usually associated with urticaria. There is release of histamine from mast cells and other inflammatory agents into the bloodstream as a result of the allergic reaction leading urticaria. There is also dilatation and increased permeability of blood vessels leading to the swelling of the cutaneous or mucosal tissue (angioedema). Angioedema and urticaria in some patients are not mediated by antibodies but due to direct stimulation of mast cells to release histamine.
Several drugs (like aspirin, opioids, dextran, NSAIDs, ACE inhibitors) and several other agents like fish, seafood, egg, milk, food additives and preservatives, insect bites and animal dander can lead to urticaria or angioedema.
Allergic Contact Dermatitis
Allergic contact dermatitis is a type IV (delayed) hypersensitivity reaction to allergens. The lesions are reddish and itchy and usually develops in the area exposed to the allergen. These lesions eventually settle once the allergen is removed, and may also require medical treatment. Fine scales on the skin and sometimes hyperpigmentation may be observed in the affected area even after the allergic reaction resolves.
Drug or Food Allergies
Food and drug allergies are very common often characterized by itching in and around the mouth and non-specific gastrointestinal symptoms like abdominal pain, nausea, vomiting, and diarrhea. It can also lead to rash, urticaria, angioedema, and anaphylaxis.
Several common food items and drugs can lead to allergic reactions. Skin allergy tests should be done before drugs known to cause allergic reactions are prescribed or administered. Skin patch tests may help identify food allergies coupled with the findings of an elimination diet and food diary. Avoiding the offending agent is the best approach for managing known drug or food allergies.
Desensitization to certain allergic drugs may be carried out when there are no drug alternatives. In such patients, desensitization can be attempted by starting the offending drug at very small doses and then gradually increasing the dose over a period of few hours to the full therapeutic dose. The procedure should be done only under medical supervision as there is a risk of anaphylaxis before desensitization is achieved.
The slow administration of the allergic drug allows slow stimulation of mast cells and gradual release of histamine at very small quantities which the body can tolerate. The activated mast cells are soon exhausted thereby allowing for further administration of the drug in therapeutic dose. The patient is desensitized but only during the administration of the drug.