Houses and apartments can lodge a large number of allergens (house dust mites, mould, etc.), which can cause allergies all year long.
While allergies are frequently considered as seasonal, our homes can lodge a vast array of allergens which can cause allergies all year long.
Indoor allergies cause symptoms ranging from psychological symptoms (fatigue, irritability, poor sleep, negative effect on concentration and performance), allergic conjunctivitis (itchy, red and watery eyes), allergic rhinitis (sneezing, blocked or runny nose, swelling and itching in the oral area) to allergic asthma with dry cough and shortness of breath.
The most common indoor allergens include :
House dust mites
House dust mites, which are part of the spider family, measure between 0.2-0.4mm and are present in all households where they tend to be more numerous in bedding, upholstery, carpets, etc.
House dust mites are one of the major causes of allergic rhinitis with symptoms such as congestion, sneezing, a dry cough or bronchitis which can lead to asthma. House dust mite allergies are perennial.
Allergic rhinitis currently affects more than 500 million people worldwide. Patients with allergic rhinitis are three times more likely to develop asthma than other people, and the risk for patients with house dust mite-induced allergic rhinitis is about six times higher than those whose allergic rhinitis is caused by grass pollen (Sources: Bousquet J, Khaltaev N, Cruz A, et al. Allergic Rhinitis and its Impact on Asthma (ARIA) 2008 update (in collaboration with the World Health Organization, GA(2)LEN and AllerGen). Allergy. 2008 Apr; 63 Suppl 86:8-160. - Brożek JL, Bousquet J, Agache I, et al. Allergic Rhinitis and its Impact on Asthma (ARIA) Guidelines – 2 2016 Revision, Journal of Allergy and Clinical Immunology (2017), doi: 10.1016/j.jaci.2017.03.050. - 3 Linneberg A., Henrik Nielsen N., Frolund L, et al. The link between allergic rhinitis and allergic asthma: a prospective population-based study. The Copenhagen Allergy Study. Allergy. 2002 Nov; 57(11):1048-1052. - 4 Calderon M. A., Linneberg A., Kleine-Tebbe J., De Blay F., Hernandez Fernandez de Rojas D., Virchow J. C., Demoly P. Respiratory allergy caused by house dust mites: What do we really know? J Allergy Clin Immunol. 2015 Jul;136(1):38-48.)
Allergies to cats are the most common type of allergy to dander. And represent two thirds of allergies to pets. Contrary to common belief, what triggers an allergic isn’t pet hair but a substance (Fel d 1) found on the pet’s fur.
This protein (or allergen) is produced by the skin of felines and is also present in their saliva, urine, tears and dander.
The allergen can be found throughout homes, in bedding, upholstery, rugs and is suspended in the air. Cat hair can also be transported by clothes and shoes. The allergen can be found in significant quantities even in a home with no cat, in class rooms for example.
Individuals allergic to cat can inhale significant quantities of the protein without even knowing it and children with a predisposition towards allergies can be sensitized to cats without being in direct contact with one.
Sensitization to dogs is less common that cat allergies. As with cats, the allergenic protein (Can f 1) is present on dog fur but is less allergenic.
Other pets can also trigger allergic reactions:
- rodents: guinea pigs, hamsters, mice, rats and rabbits
- exotic pets: gerbils, chinchilla, reptiles, arachnids, amphibians
- birds: parrots, canaries, parakeets
- farm animals: cows, horses, goats, sheep
Mould is composed of microscopic fungi that are present in the environment. Fungi can be found both indoors in damp areas (bathroom, kitchen, etc.) and outdoors (fallen leaves, compost, grasses, etc.). The spores released by the fungi can be carried by wind and dew. Mold can also develop on foods (bread, cheese, fruit and vegetables).
The microscopic size of fungi spores, which ranges from 3 to 10µm), enables them to easily penetrate the respiratory tract.
Mould can trigger respiratory allergies, both on a seasonal and perennial basis, such as allergic rhinitis, conjunctivitis and asthma.
The most common moulds which trigger allergic reactions are:
- alternaria alternata (indoor and outdoor mold)
- penicillium and cladosporium (which are present outdoors but predominant indoors)
- aspergillus: a type of mold which can trigger immediate reactions (sneezing, cough, skin rash) as well as more critical reactions such as pulmonary aspergillosis (pulmonary disease)