There has been a marked increase in the prevalence of allergic diseases since the industrial revolution. The hygiene hypothesis, which suggests a link between hygienic standards and reduced exposure to microbial substances during childhood, may partially explain this observation.
The prevalence of sensitivity to at least one allergen in school-aged children continues to rise and is approaching 50%.
There are several different types of allergies that are relevant when discussing the epidemiology of allergies disease. These include allergic rhinitis, drug allergy and food allergies.
On a global basis, allergic rhinitis is estimated to affect between 10-30% of the total population. Some degree of sensitization is indicated by the presence of IgE antibodies (immunoglobulin E antibodies produced by the immune system that target immune cells causing chemical release leading to an allergic reaction). IgE antibodies to environmental proteins, is evident in up to 4 in 10 individuals.
17.6 million adults were diagnosed with hay fever in 2012, which accounts for approximately 7.5% of the total population. In the same time period, 6.6 million children (9%) experienced symptoms of hay fever.
It is estimated that 7.8% of adults in the United States are affected by allergic rhinitis, also commonly known as hay fever.
Ethnicity appears to have an effect on the probability that an individual will be affected. Children with fairer skin are more likely to have had hay fever than those with darker skin (10% compared to 7%).
Adverse drug reactions are quite common and are thought to affect up to 1 in 10 of the general population worldwide. To further this, the relative risk is approximately double for hospitalized patients.
The incidence of cases of anaphylaxis that result in fatal outcomes may also be linked to drug allergies. In fact, drugs may be accountable for 1 in 5 of anaphylactic deaths.
The most obvious signs of an allergic reaction to a drug are fever, rash or urticaria, also known as hives, which presents as bumps or wheals on the skin. The risk factors for drug allergy include:
- Type of drug
- Dose and duration of administration
- Genetic factors (e.g. HLA type and Acetylator status)
- Concurrent health conditions
A large study of almost 40,000 children found that 8% have an allergy to a food, and 30% of these have multiple food allergies. Furthermore, more than a third of children with a food allergy have a history of severe allergic reactions.
In the United States, it is estimated that 3.5-4% of the general population exhibits IgE-mediated food allergy or sensitivity.
The most prevalent food allergen is the peanut, closely followed by milk and shellfish. Common food allergies include:
- Tree nuts (e.g. walnuts, almonds, pine nuts, brazil nuts, pecans)
- Grains with gluten (e.g. wheat, barley, rye, oats)
The severity of these allergies can vary significantly and some individuals may not experience significant effects with dietary intakes, although a sensitive response is observed in an experimental testing environment.
Allergies in the Population: The Eden Epidemiological Study Professor Thomas L. Diepgen