What are Allergies?

By Dr Ananya Mandal, MD

The term allergy encompasses a wide range of conditions; it is not a disease in itself.

History of allergies

In 1906 Clemens von Pirquet was the first to describe allergies as a changed or altered reaction of the immune system in response to exposure to foreign proteins.

These days the term allergy – medically termed hypersensitivity, signifies an exaggerated reaction to foreign substances.

The external substances that provoke allergies are called allergens. These can be inhaled, swallowed, injected or come in contact with eyes, airways or skin. (1-5)

How common are allergies?

Allergies are quite common in the population. In the United Kingdom a quarter of individuals suffer from an allergy at some time in their lives and many of these are children. This number is on the rise.

While increasing pollution is considered to be one of the reasons, there are theories that growing up in cleaner and more germ free atmospheres could be responsible for the over-reactivity of the immune system to generally harmless foreign proteins.

In general being allergic often runs in families. This is called atopy.

Allergies and their complications are expensive. According to the Asthma and Allergic Foundation of America (2002) allergies are the sixth largest cause of chronic disease in the United States. Yearly allergies cost an estimated $18 Billion.

Types of allergen

Allergens that may be life threatening in allergic individuals are usually harmless in the non-allergic. Common allergens include:

  • house dust mites
  • mould
  • grass and tree pollen
  • pet hair

Mould may be fungal spores present in damp areas. Pet skin flakes and hair from cat, dogs or hamsters may be allergenic.

Food allergens

Food allergens include:

  • nuts
  • fruits
  • cow's milk
  • hen eggs
  • wheat
  • seafood
  • soya
  • gluten etc.

Skin allergens

Skin allergens or contact allergen include:

  • latex
  • nickel
  • rubber
  • preservatives
  • dyes like hair dyes etc.

Other allergens

Allergies might be caused due to Wasp and bee stings and also due to drugs especially antibiotics like penicillin or other drugs like aspirin and anaesthetics.

What happens when the body is exposed to an allergen?

When exposed to the allergen the body fights off the protein by forming antibodies. This is called the immune response.

When a person comes into contact with the allergen again the body’s immune response “remembers” and produces the same antibodies in large amounts. This causes the release of chemicals like histamine etc. in the body and a full blown allergic reaction.

The histamine is released from the mast cells present in lungs, nose, skin or intestines. This may lead to swelling and inflammation.

Symptoms of allergic reaction

Allergic disorders range from asthma, eczema, hay fever etc. Symptoms of an allergic reaction include:

  • itching
  • runny nose and eyes
  • wheezing
  • coughing
  • shortness of breath
  • sneezing
  • skin rashes

Severity of symptoms depends on the amount of allergens the person is exposed to. In most severe cases there may be anaphylaxis. This is characterized by swelling of the throat and lockage of the airways that may be life threatening.

Diagnosis of allergies

Diagnosis of an exact cause of allergy is important. This is made by a skin prick test using multiple potential allergens to check for the exact cause of allergy.

Treatment of allergies

Allergies are best treated by prevention. The patient is advised to avoid the possible allergens as detected by the diagnostic tests. This may involve avoiding certain foods or keeping clean and dust mites and pets away.

There are medications that cure the symptoms of allergies. However, these medications do not cure the tendency for allergies.

Reviewed by , BA Hons (cantab)

Further Reading

Last Updated: Oct 7, 2014

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