Allergy

Allergy comes from the Greek, and means altered energy. It is a condition of hyper- immunity. It means that the immune system has become sensitised to something we come into contact with (called an allergen because it produces an allergic response). Usually this involves the release of a chemical called histamine, which is stored in cells called mast cells which are spread throughout the body, particularly around blood vessels, in the skin and in the mucous lining of the nose and throat and lungs, and in the intestines. Mast cells have molecules called receptors on their surface. When we come into contact with an allergen, some of the circulating lymphocytes produce antibodies, called IgE. The antibodies combine with the receptors, and the mast cell is said to be sensitised. The allergen combines with the IgE-receptor complex and thereby activates the mast cells, causing them to release histamine and other chemicals, which together invoke an inflammatory response. Under normal circumstances that’s the end of the matter (and of the allergen - it’s destroyed), but in some people the response is excessive. The effect of this depends upon the tissue involved: if it's skin then it may produce an eczematous rash (see the skin section); if it’s pollen that we breathe in it may cause the sneezing and running eyes of hay fever, or the wheeze and shortness of breath of asthma. Serious allergy may produce a severe generalised response called anaphylaxis, where a patient may collapse with shortness of breath and very low blood pressure. This is may be a consequence, for example, of nut allergy (a condition which is becoming increasingly common, for reasons which are obscure).

While it is sometimes possible to avoid those things that we are allergic to (people with nut allergy know they must avoid nuts) it can be difficult with things like pollens and house dust mite, which are everywhere. Antihistamine treatments can be used to suppress the effects of histamine. Steroid based treatments (creams for the skin and sprays for the nostrils) can reduce the inflammatory response - and sometimes may need to be taken by mouth. Those who suffer anaphylactic type reactions to allergens such as nuts or wasp stings need to have ready access to adrenalin injections, which can be life-saving. (There should be one available wherever a susceptible child spends a significant amount of time, such as the playschool). Occasionally it may be possible to desensitise those of us who have hypersensitivity, though unfortunately not all.

Food allergy may be mediated by a similar mechanism - as occurs with some people, with eggs or seafood - but it may involve other mechanisms, such as occurs in coeliac disease (see the digestive tract) where the little finger like projections in the small bowel become stunted after exposure to foods containing gluten. It may be easy to recognise the food involved if symptoms appear immediately after exposure, but some symptoms, particularly in children (irritability, colic and tiredness, hyperactivity) can be non-specific and therefore make the culprit difficult to pin down. A trial of exclusion may assist.

It is not fully understood why we develop allergies. In some there is a strong family history of hypersensitivity, with many members suffering from disorders such as asthma, eczema and hay fever. These are families who produce large amounts of the antibody called IgE, and they are described as ‘atopic’. An increasing number of people are developing these conditions without a family history, so it is felt that there are environmental factors, including possibly lifestyle, which play a part.
 
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The information provided by WIS is for guidance only. Whilst it is based upon the expert advice of leading professionals, and extensive research, it is not a substitute for diagnosis by a qualified professional. Always consult your doctor, pharmacist or qualified practitioner before making any changes or additions to prescribed medication.