Q What is an allergy?

A An allergy is a hypersensitive reaction to one or more substances which are normally harmless, these substances are known as allergens. Grass pollen, dust mites, peanuts and nickel are common allergens. Many of these substances trigger the body to produce a harmful antibody called immunoglobulin E (IgE) which causes symptoms such as sneezing, itching, rashes and falls in blood pressure. Allergic reactions also take place in situations where IgE is not produced.

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Q What are the statistics on sufferers?

A 30 percent of the population in Briton suffers from an allergy (40 percent in children) and this number is increasing. Britain has the highest asthma numbers in the world, and depending on which source you consult, is near the top of the list for eczema and allergic rhinitis. In 13 to 14 year olds, 32 percent report symptoms of asthma, 9 percent have eczema. 40 percent have allergic rhinitis.

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Q What are the causes?

A Broadly causes fall into four areas:

- Increased exposure to allergens and air pollutants.

- Over-use of antibiotics and other drugs

- Reduced fruit and vegetable intake.

- Reduced early life exposure to bacterial products, and an alteration in bacterial colonisation of the gut have all been blamed.

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Q What are the most common types of allergy?

A The five most common types of allergy show either acute reaction or delayed allergic reaction:

ACUTE

Pollen: Seasonal rhinitis (hay fever), occurs in April to August or September. Affects between 5 and 20 percent of the population. Caused by:

- Grass pollen, 90 percent.

- Tree pollen, especially birch to which 15-25 percent of hay fever sufferers are sensitive.

- Weeds, mugwort, nettles, docks.

- Wind-pollinated flowers such as daisies.

- Spores, fungi, mushrooms and moulds.

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Dust mites: perennial rhinitis (constant cold), occurs all year round, caused by dust mites present in all houses, especially beds. Caused by:

- Animal urine.

- Animal dandruff.

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Food: eight foods account for 90 percent of allergic reactions. They are peanuts, tree nuts (including walnuts, almonds, cashews, pistachios and pecans), fish, shellfish, eggs, milk, wheat and soy. The reactions are:

- True food allergy. IgE reaction to peanuts, thought to effect up to 3 percent of the population.

- Food intolerance; mimics the symptoms of a food allergy.

- Food toxicity.

- Food aversion.

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DELAYED ALLERGIC REACTION

Metal: nickel allergy. This is most common in adult females with 10 percent of women suffering contact dermatitis.

Drugs: penicillin.

Want to know more?

From the Times Online archive: Dr Thomas Stuttaford - Answers your questions on allergies | Allergy that can threaten lives | Answers your questions on hay fever

Researched and compiled by Jessica McArdle

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