allergen pronunciation and definition

Page reviewed by Dr Elena Salagean

An allergen is any substance, often harmless to most people, that can cause an allergic reaction in susceptible individuals. These reactions vary and occur when the immune system mistakenly identifies a normally harmless substance as a threat and mounts a defense against it. Allergy testing can be performed to almost all known allergens, though the availability of this may vary for the ones that are rarely encountered.

The word “allergen” dates its origin to the early 20th century when it was first used to describe a substance that can induce an allergic reaction. It essentially comes from the term “allergy” with a suffix “-gen” added to it to denote that it is “produced by” an allergy.

Where do allergens come from?

Any substance can become an allergen. Allergens are found in food, in the air around us, in medication, and in other sources. Common allergens include pollen, dust mites, mold spores, pet dander, food (such as all types of nuts, shellfish, milk, eggs, etc.), and insect stings (spiders, wasps, bees etc.). When an allergen enters the body, it triggers the production of antibodies by the immune system, leading to an allergic reaction.

What are the different types of allergens?

Broadly speaking, you could categorise some of the common allergens as below. This is not an exhaustive list of course.

  • Environmental or Aeroallergens: Pollen, dust mites, mold spores, and pet dander are common triggers of respiratory allergies.
  • Foods: Nuts, shellfish, dairy, and eggs are among the most common food allergens.
  • Insect Stings: Bee and wasp stings can introduce venom into the body, causing allergic reactions in some people.
  • Medications: Certain drugs, like penicillin, can provoke allergies in susceptible individuals.
  • Chemicals: Components found in cosmetics, detergents, rubber and dyes can lead to contact dermatitis.

What is an aeroallergen?

An aeroallergen refers to any allergen that is airborne around us.

Aeroallergnes can include pollen, house dust mites, mould spores, pet dander, and so on. The majority of allergens are in fact potential aeroallergens.

The most common allergens around us will vary depending on the environment.

A humid and warm indoor environment makes it more favourable for house dust mites and mould spores to accumulate for example. Any humidity over 60% increases the likelihood of a higher indoor dust mite and mould spore concentration. If you find that the humidity is raised inside your own house, the best solution would be to try a dehumidifier. Simply by doing this, you might sometimes notice an improvement in your allergy symptoms.

Similarly, a garden our outdoor space with flowers and perhaps freshly cut grass will be high in pollen, another type of aeroallergen.

Diagnosis and Management

Identifying specific allergens that one might react to is the first step in managing allergic reactions. Allergy testing, performed by healthcare professionals, can then pinpoint the substances to which an individual is allergic. This is often done by either skin prick testing or by IgE RAST testing. A skin prick test is the gold standard, but this may not be immediately available in general practice. It is usually performed by specialists in the allergy clinic only.

Once the responsible allergen has been identified, avoiding these allergens and preparing to treat accidental exposures is key to managing allergies effectively.

Other longer-term solutions include immunotherapy for allergies. This can be an effective way of almost curing someone from an allergy, by dampening their immune system reaction to that specific allergen.