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Food allergies in children

Eating certain foods can trigger the body's immune system to mistakenly react when it shouldn't do, causing side effects that can range from skin problems to a possible life-threatening condition known as anaphylaxis.

Food allergies are most common in under-3s, with around 1 in 14 children in this age group having one or more food allergies.

What causes a food allergy?

The immune system produces antibodies: a type of specialised protein to protect the body. These antibodies can identify threats to the body from foreign invaders such as bacteria and viruses.

Normally when they come across a threat, the antibodies send a signal to the immune system to get into action. Chemicals are released to kill the intruders and stop an infection spreading.

When there is a food allergy, a protein in the food is wrongly targeted as a threat, triggering the immune system to respond. The antibody known as immunoglobulin E (IgE) is most often involved, and it releases several chemicals, with histamine being the most important one when it comes to an allergic reaction. The histamine causes small blood vessels to expand, the surrounding skin to swell and the skin to itch. There may be excess mucus in the nasal passages.

Histamine is normally released to only certain areas of the body such as the mouth, throat or skin. However, the possibly life-threatening condition known as anaphylaxis can occur if the immune system releases huge amounts of histamine into the blood.

If the IgE antibody is not involved, the reaction is referred to as a non-IgE-mediated food allergy. In this case the immune system response is limited mostly to the digestive system and skin.

Is food intolerance the same thing as a food allergy?

These are two separate conditions.

Food intolerance occurs when there is a difficulty in digesting a food, not because of an allergic reaction. In lactose intolerance for example, the body does not produce enough of the enzyme lactase, a chemical that helps break down the milk sugar lactose. The lactose is then fermented by naturally occurring bacteria in the body (much like yeast in brewing beer), which causes the symptoms.

Unlike with an allergy, the symptoms of food intolerance normally occur several hours after eating the food and are never life-threatening. While even the tiniest particle of food can trigger an allergic reaction, some food can be consumed without a reaction in food intolerance.

Who is at risk of developing a food allergy?

While scientists are still unsure why food allergies occur, they have identified risk factors for having a food allergy. These include:

  • Family history: A child is at higher risk of developing a food allergy if one of his or her parents or siblings has a food allergy or other allergic condition such as asthma or eczema.
  • Other allergic conditions: A child born with asthma, atopic dermatitis ( eczema) or other allergic conditions is more likely to develop a food allergy.

Babies with eczema are particularly prone to food allergies, and the younger the baby and more severe the eczema, the greater the likelihood of the baby having a food allergy.

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