Under attack

Have you ever had a runny and itchy nose, watery eyes with redness and swelling? Though most of these symptoms occur in other diseases also, you may be suffering from an allergy or an allergic disorder, says DR. G.S. KAILASH.

AN allergy is a reaction to harmless substances. These may be pollen grain, spores of fungi, dust, foods items like eggs, fish, nuts and pet fur.

The substance that triggers an allergic reaction is called an allergen or an antigen. In response to the attack of the allergen, the body produces chemicals called antibodies. When an antigen and an antibody meet and react, the process is called an antigen-antibody reaction. This reaction causes an inflammation of the tissue where the reaction has taken place and causes a simultaneous release of many toxic chemicals like histamine from body cells.

Chemical substances, such as histamine, are normally stored in mast cells in the tissues of the body, including the nose, eyes and skin. People prone to allergies form antibodies IgE, against pollen, dust mites and other allergens. These antibodies attach themselves to mast cells and combine with the allergens to cause the release of histamine and other chemicals from the mast cells. These in turn cause allergic responses like itching, sneezing, nasal congestion and a running nose.

The chemicals damage the surrounding tissue leading to the many symptoms of allergy. Depending on the site of the reaction, the sufferer will experience different symptoms. For example, if the site is the lining of the nose, the person may experience a runny nose, watery eyes and lots of itching in the nose. If the reaction occurs on the skin, he will experience symptoms like reddened or swollen skin with lots of itching.

Allergies are common, with one form or another affecting nearly one-third of the population. Despite these problems being so common, misunderstandings about allergies are frequent and misinformation is rife. The number of ways in which allergic disorders can present themselves may be partly responsible for this confusion. An allergic reaction may occur in the nose and cause rhinitis, or it may take place on any part of the skin causing it to become red, hot and swollen with itching. The problems caused by an allergy may be trivial, such as a nettle rash, or life-threatening, such as anaphylaxis.

Allergies often run in families. There are two key factors that determine whether you will develop an allergic problem. The first is your genetic make-up. Most allergies are genetic. This is called atopy. If either or both your parents have a certain type of allergy, chances are that you will also suffer from it. The second factor is your exposure to allergens. In most common allergies, you need to have encountered the allergen early in life.

Different kinds of allergens

Pollen allergens

Pollens are the male seeds of plants like grasses, weeds and trees. They are invisible to the naked eye. These pollen grains contain a large number of proteins, which cause the reactions. So if you know you are allergic to pollen be careful while walking in a garden or in the woods.

Mite allergens

The most common mite allergens are their enzymes. House-dust mites are tiny creatures found in dust. The most common species is called Dermatophagoides pteronyssinus. Mites are normally harmless. However, allergic individuals can become sensitised to even small concentrations of dust mites. Dust mites are found everywhere in the house (but mainly in carpets and beds).

Fungal allergens

The most common mold allergens are Aspergillus. Allergic portions are the proteolytic enzymes. Fungal allergens have been found in large numbers in the air and in damp places. They are also found in plant matter. They are responsible for allergies like seasonal rhinitis and asthma. Fungal spores are abundant, and also produce allergens.

Insect allergens

Some people may get an allergy even from insect stings. Bee and vespid venoms contain a number of allergy causing or inflammatory agents like histamine, serotinin and various toxic peptides together with various proteins which are recognised as antigens.

Food allergens

Many children develop food allergies towards foods like cow's milk and eggs. Proteins are responsible. Food allergies are commonly misinterpreted as food intolerance.

Different kinds of allergies

Hay fever and non-seasonal or perennial allergic rhinitis

Rhinitis is the inflammatory disease of the upper respiratory system including the nose, affecting nearly 10 per cent of the population. Hay fever is caused by a reaction to the pollen of certain grasses and flowers. Allergy sufferers get an attack of rhinitis if the concentration of pollen in the air increases beyond a threshold. Weather conditions may have an influence on the concentration of pollen in the air. Hot, dry weather and the wind help pollen to disperse. These are the factors which make rhinitis worse. Rain, on the other hand, reduces pollen.

Rhinitis is basically of two types - seasonal and perennial. The first is because of pollen released during summer. Symptoms of hay fever or seasonal allergic rhinitis include itching of the eyes, the nose and throat, inflammation of the mucus membrane of the nose leading to a blocked or runny nose, sneezing and cough.

Perennial allergic rhinitis

Some types of allergies can occur any time of the year, and may be caused by the pollen grains of perennial species of trees and plants, house dust mites, animal hair and chemical substances.

Symptoms are similar to seasonal allergic rhinities. Nasal congestion (blocked nose and rhinorrhoea (runny nose) are common and are more severe than seasonal allergic rhinitis.

Allergic asthma

Asthma, also known as bronchial asthma, consists of repeated attacks of breathlessness and wheezing. When an allergen attack causes an allergic reaction, histamine and other chemical substances are liberated and these cause the bronchial wall muscles to constrict, the mucus membrane of the bronchial wall to swell and increased secretion of thick mucus which blocks the bronchial tube. The patient finds it hard to breathe. Asthma affects only those people with bronchial hypersensitivity, i.e. their bronchi are over sensitive. Causative allergens may be pollen grain, animal hair, household dust, mildewed food and insect venom. Certain individuals are prone to develop asthma due to genetic factors.

The most important symptom of asthma is dyspnoea (shortness of breath). Other symptoms include wheezing, persistent breathing difficulties and chronic coughing.

Allergies to insect stings

Bee and wasp stings can bring about allergic reactions. A bee cannot withdraw its sting once the skin is penetrated. The poison gland and some of the digestive tract enzymes are left behind in the skin causing an allergic reaction at the site.

Symptoms:

A small itchy lump appears on the skin at the site of the sting. This is a local reaction due to the venom and is not allergic. An allergic reaction in sensitive people causes a painful red swelling, which may spread and last for a few days. There are also generalised reactions with varying symptoms like urticaria, edema and vomiting.

Food allergies

Food allergies are caused by certain foods like peanuts, fish, eggs and cow's milk. A food allergy is the result of an immunological reaction with clinical symptoms. Reactions can occur within minutes after eating. Symptoms need not necessarily indicate an allergy. It may be food intolerance:

Symptoms:

Digestive problems (diarrhoea, abdominal pain, vomiting), respiratory (rhinitis, conjunctivitis, congestion) or curtaneous (pruritus, urcaria, edema).

Skin allergy

The skin is the first defensive barrier of the body against the environment. It helps us to control body temperature, prevent water loss and infections. When an allergic reaction occurs in the skin, it becomes swollen, red and itches a lot. The following are some of the forms of different skin allergies.

Urticaria

Urticaria may be caused due to various factors like food, insect stings and respiratory allergens. Some urticaria may also be due to physical forms like sun, cold and pressure. Urticaria is always charactersied by welts and flares (redness around the swollen region) with extreme itching. This may appear anywhere on the body. Itching may last a few minutes or spread over a few days, sporadically or periodically.

Atopic dermatitis

Atopic dermatitis is also called eczema. It is a common allergic reaction often affecting the face, elbows and knees. However, it can affect other parts of the skin also. Atopic dermatitis covers a range of skin problems. Symptoms include erythema (redness of the skin) and edema (swelling) are often seen. Eczema can vary from a pimple to itchy rashes. In infants, symptoms include red, scaly cheeks with fine bumps. Scratching can be severe. Atopic dermatitis in children can be an early sign of an allergy and precedes the onset of other allergic diseases such as rhinitis or even asthma.

Diagnosis of an allergy

A number of different allergens can cause allergies.

A person's medical history is important in diagnosis. It enables a doctor to make an initial selection from among the allergens most likely to be the cause of trouble. The person's family medical history, medical symptoms, habits and diet are also important. Doctors might do skin or blood tests.

Skin tests involve introduction of allergens onto the skin and looking for certain symptoms like weals or flares. Positive skin tests will indicate the presence of such symptoms. The most common blood tests involve estimation of specific IgEs in the blood. There are specific IgE immunoglobulins, which are secreted by the body's defence system against different types of allergens. The presence of specific IgEs determines the type of allergen responsible.

Management of an allergy

Allergen avoidance

If an allergen is known, avoiding it is the best possible option. Measures to avoid allergens depend on the nature of the allergen. Persons allergic to pollen should keep doors and windows closed when pollen count is high in the environment. Car windows should be raised. The individual should avoid being outdoors where specific pollen trees or grasses are in abundance.

The concentration of dust mite can only be reduced and not eliminated. Measures undertaken to reduce mite load include avoiding carpeting and heavy curtains. Floors should be made of material which should be easy to clean and walls painted with washable paint. Rugs and carpets should be exposed to sunlight once a while. Mattresses should be made of foam and covered. Feathered pillows should be avoided.

Skin cells and hair from pet animals are another source of allergens. If an individual is allergic to pets, it is advisable to keep pets outside the house or at least outside the bedroom. Spores, the reproductive cells of molds, are difficult allergens to eradicate. They are abundant during humid and warm periods. Damp areas in the home should be kept dry. All rooms should be kept properly ventilated and receive good sunlight.

Immunotherapy (desensitisation)

It involves the introduction of controlled quantities of allergens into individuals susceptible to them. Immunotherapy is useful in patients sensitive to pollen. However, the process involves identifying the allergen which, many a time, is not possible. The therapy is spread over time as long as three to five years, to have the desired effect.

Therapy

Drug therapy is used basically to treat symptoms of an allergy. The choice of drug will depend on the type of allergy and medical history of the individual. Drugs may be used alone or in combination and should be taken with medical advice.

The writer is medical director, Asthma and Allergy Clinic, Mylapore, Chennai.

October 16 was observed as World Allergy Awareness Day.

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