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What is an allergy?

1 in 4 people in the UK are affected by allergies – and each year this number is rising – with as many as half being children. But what actually is an allergy?

We often talk about allergies without using the term correctly or knowing exactly what they are. An allergy is defined as the body’s overreaction to a substance it is exposed to, through eating, breathing or via skin contact. Typical substances – called allergens – that might trigger an allergy include pollen, eggs, nuts and gluten (a protein found in cereals such as wheat). In a non-allergic person the body will not react to the allergen. But in the allergic person, the body’s immune system will overreact, creating antibodies. The antibodies remain in the body, ready to react if that person is exposed to the allergen again. This stage is called ‘sensitisation’ and the allergic person remains unaware they have an allergy.

The next time the allergic person comes into contact with the allergen the antibodies kick in and cells, including those in the skin, nose, eyes, mouth, throat and stomach produce chemicals including histamine. These chemicals cause the symptoms of allergies – from mild reactions such as sneezing, itchiness, inflammation, tummy ache, vomiting and diarrhoea – to more severe symptoms including swallowing difficulties, shortness of breath, a drop in blood pressure, chest pain and anaphylactic shock.

Do I have an allergy?

The risk of having an allergy is greater if a close relative has or has had an allergy or asthma, if you have asthma, or if you are a child. But how do you know if your symptoms are those of an allergy or of an intolerance, and exactly what the difference is?

The term ‘allergy’ originally covered any adverse reaction to an everyday substance, but now is used specifically to define allergic reactions produced by the immune system. Those with food allergies need only a tiny amount of the food to which they are allergic to have a serious reaction. By comparison, the term ‘intolerance’ means that the immune system is not involved, despite unpleasant symptoms such as wind, stomach cramps and diarrhoea. Those with food intolerance can often eat a small amount of that food without problems.

Milk, egg, peanut, tree nuts, fish, shellfish, soy and wheat account for 90 per cent of all food-allergic reactions. While many people grow out of allergies to milk, eggs, wheat or soy, allergies to peanuts and shellfish tend to be life-long, with severe symptoms. Tree nut allergy is one of the most common food allergies and is potentially fatal. Tree nuts include walnuts, almonds, hazelnuts, cashews, pistachios and Brazils, but not peanuts, which are actually legumes, not nuts. Skin allergies occur after the skin comes into contact with an allergen such as the metals used for jewellery, fragrances (in everything from shampoos to laundry detergents), latex, chemicals in hair dye, sunscreen, household solvents and even antibiotic creams and ointments.

If you think you have allergy or intolerance symptoms, go to your GP to be tested. Typically, a skin prick test or a blood test will be used. If an allergy or intolerance is diagnosed, this site will be able to help you with advice and information.

Related Topics

Allergy Help