Allergy

What is an allergy?

An allergy is a form of hypersensitivity in which the immune system responds to substances (allergens) that are usually harmless and do not cause disease. Allergic reactions are the result of various types of exposure to an allergen:

• by inhalation (inhalation allergy), for example dust mite allergy, hay fever and asthma
• through the gastrointestinal tract (food allergy), for example to cow's milk, eggs or peanuts
• as a result of being stung by an insect (insect allergy), for example a bee or wasp
• as a result of the administration of a drug (drug allergy) such as penicillin
• through skin contact (contact allergy), for example with nickel or perfume.

What are the complaints associated with an allergy?

The complaints depend on the type of allergy. Examples are: irritated connective tissue in the eye with moist discharge, allergic cold, asthma (shortage of breath), skin abnormalities such as eczema, hives (urticaria), itchy accumulations of fluid in the skin and mucosa (angioedema) or a life-threatening general hypersensitivity reaction (anaphylaxis).

How common are allergies in the general population?

Based on the number of users of antihistamines in 2008, at least 1.2 million people in the Netherlands have an allergy; in a population of 16,500,000 people, this means that prevalence is about 7%. ⁸⁴

On the basis of records from general practice, it is estimated that about 3% of the population in the Netherlands have asthma and about 1.5% constitutional eczema. It is difficult to estimate how many people have other allergic conditions such as hay fever and food allergy. ⁸⁴

Suspected food hypersensitivity or allergy are much more frequent than proven food allergies. More than 10% of the population are thought to have food hypersensitivity. ⁴⁶⁴

Records from general practice underestimate this prevalence because GPs are often not consulted about these conditions. The one-year prevalence of allergic and non-allergic nasal allergy (rhinitis) (including hay fever) in the population is thought to be 15 to 20%. In records from general practice, the one-year prevalence of allergic and non-allergic rhinitis is 2.5% for men and 3.1% for women. Allergic rhinitis is seen primarily between the ages of 5 and 45 years, with a peak between 15 and 24 years. ⁴⁶⁵

On the basis of epidemiological surveys, it has been estimated that one third of the Dutch population have a nasal allergy (allergic rhinitis), including hay fever. The number of children with food allergies is estimated at 1.3% and the number of adults at 1.2%. ⁸⁴

How common are allergies in people with intellectual disabilities?

In the European POMONA questionnaire survey of a random sample of 1269 adults with intellectual disabilities, 6.3% had asthma. ⁸⁵  The same study found that 21% had another allergy (it should be pointed out that asthma was excluded in the question relating to 'allergy'). Merging these two prevalence rates would result in a prevalence for allergy of 27.3%.
In a study in the UK of 1097 people with intellectual disabilities, 12% had asthma. ⁸⁶ This is twice as many as in the general population. More children with Down syndrome have food allergies and asthma than children with intellectual disabilities but without Down syndrome.

A large Australian survey of 2540 people with intellectual disabilities (in which questionnaires were answered by carers and parents) found that 24% of the study sample had an allergy. ⁸⁷

A US study compared children with intellectual disabilities and children with intellectual disabilities and intellectual disabilities with autism or ADHD. All three groups of children with intellectual disabilities were significantly more likely to suffer from allergies than children without intellectual disabilities. ⁴⁶⁶