Allergy is an immunological response to substances called as allergen. An allergy may be caused by either host factors or the environmental factors. Age, sex, race and heredity are the host factors. Environmental pollution, changes in diet, levels of allergen in the environment and altered exposure to infectious diseases in childhood are the environmental factors. Allergies may be due to insect bites, medications or food.
The reason behind the varied immunological response to a certain allergen in different populations is explained on the basis of hygiene hypothesis. According to this hypothesis, people living in polluted environment are exposed to adequate pathogens so that the immune system remains busy and are not able to stimulate response against risk free antigens, therefore people in polluted environment are less prone to allergies than living in sterile environment.
Allergies are more seen in the countries with more industrialization than agriculture or traditional countries. Also allergies are more common in urban population than the rural one. Some common allergic reactions include eczema, hives, hay fever, asthma, food allergies, and reactions to the venom of stinging insects such as wasps and bees.
The symptoms of allergy depend on the affected site. For air borne allergies it may be inflammation of the nasal passage, sinusitis, sneezing, coughing, runny nose, itching, constriction of the bronchi, wheezing, dyspnea, asthma, constriction of the airway, reddening and burning of eyes, fullness of ears, hearing impairment, rash on the skin.
Pain in abdomen, vomiting, bloating or diarrhea are the symptoms of food allergies.
Allergies due to insect stings, antibiotics or medications evoke systemic response and multiple organs or systems like digestive system, respiratory system and circulatory system are involved in it. The contact of allergen with skin causes skin reaction called as contact dermatitis or eczema. Skin allergies frequently cause rashes, or swelling and inflammation within the skin, what is known as a "wheal and flare" reaction characteristic of hives and angioedema. They vary from mild symptoms like hay fever, rash or conjunctivitis to more severe reactions like anaphylactic shock.
To find out the cause of allergy skin tests are done with suspected allergens. Skin tests are less expensive, simpler than blood tests and more sensitive and specific. Therefore skin tests are preferred over blood tests for diagnosis of allergy. However, skin tests cannot be done in patients on antihistamine medications for longer duration and in patients with skin diseases. Blood tests may also be done to find out the cause of allergy. Blood test measures the serum IgE (immunoglobulin E) levels. A high IgE levels is indicative of an allergic reaction.
The anti allergy medications include antihistaminics, antileukotrienes, anticholinergics, mast cell stabilizing agents and the agents that impair eosinophil chemotaxis.
Steroids like cortisone, dexamethasone and/or hydrocortisone are also often used as conjunction therapy.
Immunotherapy involves desensitization or hyposensitization of the patient by a process of gradual vaccination with progressively larger dosage of the allergen resulting in either hyposensitization or complete desensitization. Due to this there is lowered immune response or no immune response at all against that particular allergen. Monoclonal anti IgE antibodies and sublingual immunotherapy are some more treatments available for the treatment of allergy.
There may be two phases of allergic responses: immediate or acute and delayed. The acute phase may settle or may lead to late reaction. The late reaction makes the allergic response longer and there may be tissue injury.
Allergic reactions to certain allergen are very serious especially on second or subsequent exposure. They may be called as hypersensitivity or anaphylactic shock and is life threatening. For example, allergy to penicillin, in this, in sensitive individuals the second exposure may be life threatening.
If symptoms of allergy do not subside in 2-3 days, if the symptoms aggravate or if the allergic reaction is severe then it is better to contact the health care provider.
Avoiding the suspected allergen is the traditional way of avoiding allergy and still holds good for managing some allergies especially food allergies. There are several things which can control the levels of allergen. They are control of dust to control mites, vacuum cleaning, avoiding pet animals and avoiding pollens and spores of fungi. Plants have pollens as well as fungi so limiting house plants helps in preventing allergies. To avoid growth of fungi, the moisture inside the house should be reduced. Overall cleanliness and hygienic practices help in preventing allergic reactions.
