Aeroallergens and the skin

What are aeroallergens?

Aeroallergens are various airborne substances or inhalants, such as pollens, spores, and other biological or non-biological airborne particles that can cause allergic disorders. Inhalation or cutaneous contact with aeroallergens can trigger a release of proteins in the form of an allergic reaction on the skin and mucous membranes [1,2].

Airborne particles can also cause irritant reactions without causing an immunological response.

Which are the most common aeroallergens?

The most common aeroallergens causing disease are pollens and house dust mites. Pollens are derived from:

• Grasses
• Trees
• Rye
• Weeds.

Other aeroallergens may include:

• Lilies, daisies and other perfumed flowers
• Latex allergen in glove powder
• Animal dander or fur (eg, from dogs, cats, and rabbits)
• Rodent dander, fur, urine, and saliva (eg, from mice, rats, and guinea pigs)
• Cockroach debris
• Mould and fungal spores
• Cosmetics, including perfume, antiperspirants and deodorants
• Pesticide spray
• Tobacco smoke (a common irritant and a rare allergen).

Combustion product irritants include:

• Carbon dioxide (CO₂)
• Carbon monoxide (CO)
• Nitrogen dioxide (NO₂)
• Sulphur dioxide (SO₂)
• Volatile organic compounds
• Lead (Pb)
• Other particulate matter
• Ozone.

Who gets diseases from aeroallergens?

Allergies only affect susceptible individuals (see DermNet NZ's page Allergies explained) whereas irritant reactions can affect anyone.

The prevalence of aeroallergens is quite variable from one region or country to another, depending on the climate, the local plants and animals, and the degree of pollution [3,4].

Climate change has been reported to contribute to the rise of some types of aeroallergens and to a surge in allergic disorders [5–7].

• House dust mites are prevalent in developing countries.
• Pollen aeroallergens are prevalent in temperate zone countries.
• Pollen counts vary with exact location and flora, time of year, altitude, temperature, humidity, wind, electrical activity, and rain [8].

In New Zealand, the main aeroallergens are grasses [8]. The pollen season lasts for about 34 weeks beginning in July or August.

• In Scandinavia, the main allergen is birch.
• In North America, the main aeroallergens are ragweed and deciduous tree pollens.
• Olive pollen is prevalent in the Mediterranean.
• Feverfew and mugwort are important aeroallergens in Eastern Europe and India.
• In Japan, the Japanese cedar is responsible for many cases of pollen allergy.

Pollen forecast 18 February 2019, Hamilton, New Zealand

How do aeroallergens cause disease?

Although usually due to other factors, some common skin conditions are occasionally triggered or aggravated by aeroallergens [9–11]. How this occurs remains unclear (see figures 1 and 2 below for proposed mechanisms).

Induction and effector mechanisms in Type 1 hypersensitivity

Credit: Ghaffar A, Hunt R. Immunology. Chapter seventeen: Hypersensitivity reactions. Microbiology and Immunology On-line. [12].

Aeroallergen pathways

Credit: De Schryver E, Devuyst L, Derycke L, et al. Local immunoglobulin E in the nasal mucosa: clinical implications. Allergy Asthma Immunol Res 2015; 7: 321–31. [13].

Which health problems are due to aeroallergens?

Aeroallergens commonly cause allergic rhinitis, allergic conjunctivitis, and allergic asthma, and they may contribute to eosinophilic oesophagitis [14­–16].

Skin conditions due to aeroallergens are less common. These include:

• Allergic contact dermatitis (eg, when the causative allergen is Compositae/Parthenium and epoxy resin)
• Acute urticaria, angioedema, and rarely, anaphylaxis (eg, when latex allergen in glove powder is circulating in the air)
• Seasonal atopic dermatitis (eg, eczema associated with house dust mites).

Contact dermatitis to Compositae pollen

Atopic dermatitis affecting neck

Acute urticaria

Credit: Aeroallergens, reaction pathway and skin disorders (adapted from Allergy Asthma Immunol Res 2015, and microbiologybook.org) [15,16].

How is the role of aeroallergens investigated?

When a careful patient history and examination findings lead to suspicion of a cutaneous reaction to aeroallergens, investigations may include:

• Immunoglobulin E (IgE) blood tests
• Skin prick tests
• Patch tests.

How are reactions to aeroallergens minimised?

The avoidance and elimination of aeroallergen triggers can be challenging.

Pollens

Be aware of the allergenic plants in your region and monitor the local pollen forecast. Stay indoors and consider taking antihistamines and other medications when the pollen count is high.

Moulds

Thoroughly clean contaminated areas such as bathrooms, laundries, and basements. Ventilate damp areas to prevent the growth of moulds.

House dust mites

Clean and vacuum all pillows, mattresses, bed-sheets, towels, carpets, and upholstered furniture. Consider using pillow and mattress protectors to minimise house dust mites.

Animal dander and fur

Avoid contact with animals if possible. Bathe pets regularly.

What is the treatment for aeroallergen allergy?

The treatment of an aeroallergen allergic disease depends on the symptoms experienced.

• Antihistamines are taken for allergic urticaria, allergic rhinitis and allergic asthma.
• Topical corticosteroids and emollients are used to treat eczema.

Immunotherapy for allergic diseases (whether serial subcutaneous injections or sublingual) can reduce the reaction to aeroallergens in some patients.