allergens

see also:

• allergy and hypersensitivity reactions
• anaphylaxis
• asthma

• allergen exposure in sensitive individuals may cause allergic rhinitis, conjunctivitis, pruritis and asthma
• rarely, it may cause anaphylaxis
• the main rule is to avoid allergens where possible, or at least minimise the exposure load
• acute therapy of rhinitis/conjunctivitis is usually with antihistamines
• if avoidance is not possible, systematic desensitisation may help

• many people are allergic to various pollens and may suffer hay fever or asthma
  • in Melbourne, this is usually due to high pollen counts from rye grass in Nov when the north wind blows, and these can lead to thunderstorm asthma events
• most plants that cause issues are not native to Australia and their pollen readily becomes wind blown (most Australian native plants have pollen spread by insects or birds and are not readily airborne, although could cause issues when at close proximity to flowers)
• wind-borne pollens
  • perennial rye grass
  • trees (usually the male versions) such as Cypress, Box Hedges, Pine Trees, Alder, Beech, Birch, Ash, Willow, Elm, Olive, Mulberry, London Plane, Poplar, Maples, Walnut, Mango and White Cedar
• close contact pollen allergens
  • Callistemon (bottlebrush)
  • Melaleuca
  • Amaranth (pigweed), chamomile, chrysanthemums, daisies, ordinary sunflowers
  • jasmine vine, juniper, wisteria
  • weeds such as Cocklebur, ragweed, Russian thistle, sagebrush, Pellitory (Parietaria judaica or asthma weed)
• contact dermatitis or urticaria
  • Rhus trees (Toxicodendron)
  • Bermuda/couch grass
  • Melaleuca
  • many others

• the microscopic sized common household dust mites live in pillows, bedding, carpet, etc, particular in warm humid homes
• their bodies and faeces are major sources of allergens which become aerodynamic particles 10 µm or larger in diameter and remain in undisturbed air for 30 minutes or less
• the major sources of dust mite allergens are the group 1 allergens Der p 1 and Der f 1
• levels of 10 mcg/g of dust induce allergic symptoms or asthma in sensitized persons, but lower levels may also cause symptoms in these individuals¹⁾
• ~25% of homes in USA have levels high enough to induce asthma
• reducing exposure:
  • weekly vacuum cleaning
  • weekly washing of bedding in hot water
  • reduce indoor humidity
  • impermeable woven pillow and mattress covers
  • remove carpets and upholstered furniture

• 8-10% of the population are allergic to cats or will develop allergy if exposed to cats over a period of weeks
• the major cat allergen is Felis domesticus (Fel d 1) which is produced by sebaceous glands and saliva and thus coats the cat's hair
• of those with cat allergy, nearly 2/3rds have antibodies against Fel d 4 (a lipocalin), a product of the cat major urinary protein gene and which is secreted with saliva.
• the allergen forms much smaller aerosolized particles (average size of 5 µm) than dust mites and readily coats walls and stays airborn in undisturbed air within a house for days!
• recent studies suggest adults having a pet cat for the 1st time may be twice as likely to develop cat allergy
• the proposed threshold level for sensitization by cat allergen is 1 mcg/g of dust, and the level to cause symptoms in susceptible individuals with asthma is 8 mcg/g of dust
• the allergens may remain for months in the house even after removal of the cat
• reducing cat allergy:
  • decrease your exposure:
    • ban the cat from being inside the house, or at least ban it from certain rooms such as bedrooms and close doors to prevent aerosols coming into the bedrooms
    • neutering male cats seems to decrease allergen secretion
    • shampoo cat weekly to reduce level of allergens on fur although most cats hate bathing and there may not be any evidence to support its benefits
    • brush hair regularly to remove and dispose loose hair
    • keep windows open as much as possible to ventilate the house
    • remove items that trap allergens such as carpets, rugs and pillows
    • clean regularly to remove dust using HEPA filters (have a non-allergic person do the vacuuming!), however, there is no evidence that vacuuming helps and the sweeping motion will disperse allergen into the air so choose a windy day with the windows and doors open.
    • wash hands frequently especially after touching the cat, and before touching your eyes, nose or mouth
    • don't forget your contaminated clothes will increase the load on your hands as well as take the allergen into your bedroom
  • treat symptoms:
    • antihistamines
  • systematic desensitisation can be useful for cat allergy and is designed to increase tolerance:
    • subcutaneous injections of modified allergens
    • 2025: Allergen Immunotherapy with Depigmented–Polymerised Cat Allergoid Is Safe and Well-Tolerated in Patients with Allergic Rhinitis/Rhinoconjunctivitis
  • make sure it is the cat you are allergic to rather than the brand of cat litter, etc.

• the major dog allergens, Canis familiaris 1 (Can f 1) and Canis familiaris 2 (Can f 2), have physical properties similar to those of cat allergens.
• dogs should be washed twice a week if the owner is sensitive to them

• only 5 of the 3500 known species are important indoor allergens
• similar aerosol characteristics to dust mite allergens
• may partly explain increased incidence of asthma in inner urban areas or substandard infested apartments
• allergic reactivity to proteins from cockroaches may reflect sensitization to a broader spectrum of cross-reactive allergens such as tropomyosins, arginine kinases, Bla g 5 (glutathione S-transferase) and Der p 11 (paramyosin) reflecting shared structural epitopes across cockroach, mite, and other invertebrate allergens. A 2026 study showed sensitization patterns also extended to edible insects such as locusts, crickets, and mealworms, as well as storage mites, dust mites, seafood, and wasp species²⁾

• most of the fungi recovered from an indoor environment emanate from outside.
• certain species, such as Penicillium and Aspergillus, can be found in greater quantities inside buildings and homes.
• asthma severity has been linked to sensitivity to Alternaria species