What is an Allergy?


An allergy is an adverse reaction involving the immune system, which follows contact with a substance that is normally harmless. In many types of allergy the symptoms occur very rapidly and usually involve the part of the body that has been in contact with the harmless substance.

Most allergic reactions occur in the mouth, nose, lungs, digestive tract, or skin, So in hay fever, for example, contact with grass pollen causes a discharge from the nose and eyes, frequent sneezing and an itchy feeling in the eyes, nose, roof of the mouth, and even the ears.

The symptoms occur when the immune system, for reasons we do not understand, overreacts to a substance from which it believes the body needs protection. Such substances are known as allergens, and they can trigger an allergic reaction when they come in contact with the body, by being touched, inhaled, eaten or injected. Confusion can sometimes arise because symptoms that are similar or even identical to those produced by an allergic reaction can occur without the immune system apparently being involved. For example, frequent sneezing and a runny nose are allergic reactions when they are caused by exposure to grass pollen but not when they result from chemical irritation, such as when chopping onions, or from a common cold.

Reactions To Chemicals

Some people appear to be sensitive to chemicals that enter the body either through the skin or by being inhaled. If you are sensitive to chemicals, such as fumes from gasoline or paint, perfumes, pesticides and cigarette smoke, you may experience a number of symptoms, including migraines, fatigue, abdominal pain, rhinitis, eczema and urticaria when you some into contact with them.

Reactions to food

Many people experience various adverse reactions to food; in fact one person in six has a food allergy. Usually, it is a lifelong condition which recurs whenever the culprit food is eaten, so avoiding it is essential. Any food can be involved, but the commonest culprits are peanuts, fish, shellfish, papaya and strawberries. The trouble begins when the food comes into contact with the mouth, causing tingling and local swelling. Other symptoms include nausea, sickness and stomach cramps. An urticarial rash, wheezing and coughing may also occur. In rare cases anaphylaxis may develop.

What is food intolerance?

In food intolerance, the immune system does not appear to be involved. In addition, the symptoms which include headaches, tiredness, depression, painful or aching muscles, cold sores, digestive disorders, such as irritable bowel syndrome and arthritis, are usually less immediate and more likely to involve distant parts of the body, such as the brain. Any food can cause intolerance, but the commonest culprits are those eaten frequently, such as wheat, eggs and milk. It is best to avoid the culprit foods, but unlike the case of a food allergy, they can eventually be reintroduced.

Non allergic food reactions

Certain foods can produce symptoms similar to those triggered by an allergy or food intolerance, but the cause is entirely different. Non allergic food reactions can be difficult to treat, but your doctor will be able to help.

  • Symptoms caused by foods that contain or release histamine, which is one of the chemicals released by the immune system is an allergic reaction
  • Symptoms triggered by foods containing chemicals that act in much the same way as a drug, e.g. caffeine
  • Symptoms caused by the body’s inability to produce certain digestive secretions.
  • Symptoms of food poisoning caused by eating contaminated food

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