As written earlier, allergy is of different types depending on the mechanism of action and the offending agent (allergen). For a layman it will be easier to comprehend if allergy is classified based on the causative agent. Thus the types of allergy may be classified as given below:-
□ Dust Allergy
□ Food Allergy
□ Drug Allergy
□ Insect Allergy
□ Skin Allergy
□ Allergy due to other substances Dust Allergy
Dust allergy refers to allergic symptoms caused by inhaling (breathing in) certain microscopic particles found in the environment surrounding us. These allergens (also called aeroallergens) may be found either at home, in our place of work or while travelling from one place to another. The common aeroallergens are as follows:
□ Dust, smoke, fumes and gases emitted by polluting vehicles, industries and factories are most common aeroallergens in India.
□ Climatic conditions like high humidity, sudden changes in temperature, especially from warm to cold and smog formation are also important factors causing allergic symptoms.
□ Active and passive smoking is equally responsible for causing allergy and other symptoms of the respiratory system.
□ Pollen grains of different plants suspended in air especially on windy and rainy days.
□ Fungi and moulds found in damp and moist areas also cause allergic diseases.
□ Dust mite found at home that collect in the mattresses, furniture, carpets and rugs, bedding draperies, clothes and floor, which are inhaled while dusting or cleaning the house.
□ Inhalation of insect parts and droppings of cockroaches, flies, moths, butterflies, rats, mice, bed bugs, mosquitoes, houseflies, etc.
□ Animal allergen in the form of epithelial scales (dander), hair or feathers of animals like dogs, cats, cattle, horse, sheep, goat, duck, etc.
□ Occupational allergens like silica, asbestos, lead, nickel, coal, cotton, wool, fibres, paints, varnishes, resins, grain flour, formaldehyde, insecticides, pesticides, dyes, drugs, spices, printing ink, etc.
Food Allergy
Foods are mainly composed of proteins, carbohydrates and lipids. Usually, the major food allergens are the glycoproteins found in the food.
□ About 2-3% of infants suffer from cow’s milk allergy, which is the most common food allergy of childhood. This seems logical since cow’s milk formula is usually the first foreign substance a baby consumes, and also the digestive and immune systems of the infant are not fully developed. Most children outgrow milk allergies by the age of four and food allergies that develop after this age are usually permanent. The major allergens in milk are the caseins and the whey protein – beta lactoglobulin. The milk from goats and sheep has almost similar proteins as cow’s milk and cannot be used as the latter’s substitute.
□ Allergy to eggs is usually observed in young children and like cow’s milk allergy, fades with time. The main allergens are the egg-white proteins, ovomucoid, ovalbumin and ovotransferrin. The eggs of other poultry such as ducks are similar to that of hens and also cause allergy.
□ Seafood allergy is more common in adults than children and is more prevalent in countries with a high consumption of fish and shellfish. The major allergens in fish are flesh-proteins called parvalbumins, which are similar in all kinds of fish. Cooking does not destroy the allergens in fish and shellfish and some individuals may be allergic to the cooked and not raw fish.
□ Certain fruits and vegetables are also capable of causing allergic reactions, though very mild and often limited to the mouth (oral-allergy syndrome). The commonly allergic fruits and vegetables are apples, bananas, tomatoes, soyabean, peas, and beans. Many of these allergens are destroyed by cooking and are thus safe in allergic individuals.
□ Peanuts are one of the most allergenic food and frequently cause very severe reactions, including death. This allergy is established in childhood and is usually maintained throughout life. Traces of peanuts found in processed oils or in utensils used for serving foods, can be enough in some individuals to cause an allergic reaction.
□ Tree nuts such as walnuts, almonds, cashewnuts, hazelnuts and pistachios can cause very severe allergic symptoms, which can occasionally be fatal. Roasting or cooking cannot destroy the allergens.
□ Certain cereals like wheat, rice, barley, rye, oats and maize are also associated with allergy. The more we eat these cereals the more likely we are to suffer an allergy. Seed storage proteins such as wheat gluten and other proteins present in grain to protect it from bacteria and fungi have been found to be major allergens.
□ Food additives and preservatives like sulfites, tartrazine, monosodium glutamate are also responsible for causing food allergy.
Drug Allergy
Almost everyone in his lifetime has undergone certain unpleasant effects due to medicines. Some may develop drowsiness, others develop stomach disorders like diarrhoea or constipation or hyperacidity and a few develop headache, giddiness, etc. These are usually the known side-effects due to overdose or drug-interactions. Drug allergy usually refers to serious adverse effects in a person, which may not have occurred while taking the same medicine earlier. The mechanism of these effects are due to production of Immunoglobulin E as in the case of other allergies. Usually people with drug allergies have a family history of allergies and may be also suffering from dust allergy or food allergy.
The medicines to which people usually develop drug allergy are as follows :-
1. Penicillin group and Cephalosporins
2. Insulin
3. Vaccines like DPT, Influenza (HIB), Tetanus, MMR Chickenpox
4. Sulfonamides (Sulfa drugs)
5. Intravenous contrast, dyes used in tests like CT Scan, MRI, IVP, etc.
6. Aspirin and other painkillers
7. Local and general anaesthesia
Insect Allergy
Usually insect bites and stings cause mild and temporary pain and swelling at the site of the bites. In sensitised individuals, allergic reactions may result in more severe local reactions as well as generalised symptoms ranging from mild to fatal responses.
The insects which usually cause allergic symptoms are as follows :-
□ Bees – honey bees, bumble bees
□ Wasps, hornets, yellowjackets
□ Fire ants
□ Mosquitoes
The risk of insect bites increases in summer and rainy weather and can occur with outdoor exposure. Incidence is more in unsanitary areas, forests and grassy areas and near the water bodies. Loose fitting clothes may entrap insects. Insects are attracted to bright colours and floral patterns and to perfumes, lotions, scented soaps and hair preparations.
Skin Allergy
Several soaps, detergents, perfumes, cosmetics, dyes and items of daily use produce allergic reactions at the site of contact. This is referred to as skin allergy. The allergic effects are more common in thinner sites like eyelids, earlobes and genital sites, and less in palms of hands and soles of feet.
The following are the allergens and the sources where they are found:-
Substance – Source
Plants – Poison ivy, poison oak, chrysanthemum, tulips, rosewood pines.
Nickel – Jewellery, watches, jean studs, bra clips.
Rubber / Latex – Gloves, condoms, clothing, shoes, tyres.
Colophony – Sticking plaster, adhesives, sealants, collodion.
Epoxy – resins Adhesives, paints, surface coatings.
Wool alcohol (Lanolin) – Cosmetics, creams, ointments, lotions, soaps.
Paraphenylenediamine – Hair dye, shampoo, conditioners.
Balsam of Peru – Perfumes, citrus fruits
Neomycin – Ointment, cream, eye drops,lotions.
Furazoline – Furacin ointment.
Potassium – dichromate Cement, industrial chemicals.
Thiomerasol – Preservatives in cosmetics, nose drops and ear drops.
Allergy – Due to Other Substances
Solar Allergy
Many people are allergic to sunlight and develop skin disease (dermatitis) within minutes of exposure to sunlight. The ultraviolet rays of the sun act as the trigger for allergic changes on the skin. Sometimes, sunscreening agents used in cosmetics such as moisturisers, lip and hair preparations and foundation make-up, accelerate solar allergy.
Allergy Towards Pets
Many people with a history of dust allergy or food allergy, who keep pets at home, have been observed to have allergic symptoms due to the pets. Dogs and cats are such faithful and lovable animals that millions of people keep them as pets at home. Majority of people play with them or bathe them or even make them stay in their bedroom, without facing any problems. But certain individuals immediately start sneezing and coughing when they enter the room where the animals are located.
Such people are known to suffer from pet allergy. The allergens in dogs are the dead skin flakes or epithelial scales and in the cat, the sebum from the sebaceous glands near the base of the tail. Hair or feathers from cattle, horse, sheep, goat, duck and other birds also have an allergic effect. Urine, saliva and bacteria of these animals as well as rats and mice can also cause allergy.