Allergen

Allergens can be found in a variety of sources, such as dust mite excretion, pollen, pet dander, or even royal jelly.[2] Food allergies are not as common as food sensitivity, but some foods such as peanuts (a legume), nuts, seafood and shellfish are the cause of serious allergies in many people.

Officially, the United States Food and Drug Administration does recognize eight foods as being common for allergic reactions in a large segment of the sensitive population. These include peanuts, tree nuts, eggs, milk, shellfish, fish, wheat and their derivatives, and soy and their derivatives, as well as sulfites (chemical-based, often found in flavors and colors in foods) at 10ppm and over. See the FDA website for complete details. In other countries, due to differences in the genetic profiles of their citizens and different levels of exposure to specific foods resultant from different dietary habits, the "official" allergen lists will vary. Canada recognizes all eight of the allergens recognized by the US as well as sesame seeds[3] and mustard.[4] The European Union additionally recognizes other gluten-containing cereals as well as celery and lupin.

Another allergen is urushiol, a resin produced by poison ivy and poison oak, which causes the skin rash condition known as urushiol-induced contact dermatitis by changing a skin cell's configuration so that it is no longer recognized by the immune system as part of the body. Various trees and wood products such as paper, cardboard, MDF etc. can also cause mild to severe allergy symptoms through touch or inhalation of sawdust such as asthma and skin rash.[5]

An allergic reaction can be caused by any form of direct contact with the allergen—consuming food or drink one is sensitive to (ingestion), breathing in pollen, perfume or pet dander (inhalation), or brushing a body part against an allergy-causing plant (direct contact). Other common causes of serious allergy are wasp,[6] fire ant[7] and bee stings,[8] penicillin,[9] and latex. An extremely serious form of an allergic reaction is called anaphylaxis. One form of treatment is the administration of sterile epinephrine to the person experiencing anaphylaxis, which suppresses the body's overreaction to the allergen, and allows for the patient to be transported to a medical facility.

SEM of miscellaneous plant pollens. Pollens are very common allergens.

The house dust mite, its feces and chitin are common allergens around the home

Common food allergens

In addition to foreign proteins found in foreign serum (from blood transfusions) and vaccines, common allergens include:

• Animal products
  • Fel d 1 (Allergy to cats)
  • fur and dander
  • cockroach calyx
  • wool
  • dust mite excretion
• Drugs
  • penicillin
  • sulfonamides
  • salicylates (also found naturally in numerous fruits)
• Foods
  • celery and celeriac[10]
  • corn or maize
  • eggs (typically albumen, the white)
  • fruit
    • pumpkin, egg-plant
  • legumes
    • beans
    • peas
    • peanuts
    • soybeans
  • milk
  • seafood
  • sesame
  • soy
  • tree nuts
    • pecans
    • almonds
  • wheat
• Insect stings
  • bee sting venom
  • wasp sting venom
  • mosquito bites
• Mold spores
• Top 5 allergens discovered in patch tests in 2005–06:
  • nickel sulfate (19.0%)
  • Balsam of Peru (11.9%)
  • fragrance mix I (11.5%)
  • quaternium-15 (10.3%), and
  • neomycin (10.0%).[11]
• Metals
  • nickel
  • chromium
• Other
  • latex
  • wood
• Plant pollens (hay fever)
  • grass — ryegrass, timothy-grass
  • weeds — ragweed, plantago, nettle, Artemisia vulgaris, Chenopodium album, sorrel
  • trees — birch, alder, hazel, hornbeam, Aesculus, willow, poplar, Platanus, Tilia, Olea, Ashe juniper, Alstonia scholaris

Seasonal allergy symptoms are commonly experienced during specific parts of the year, usually during spring, summer or fall when certain trees or grasses pollinate. This depends on the kind of tree or grass. For instance, some trees such as oak, elm, and maple pollinate in the spring, while grasses such as Bermuda, timothy and orchard pollinate in the summer.

Grass allergy is generally linked to hay fever because their symptoms and causes are somehow similar to each other. Symptoms include rhinitis, which causes sneezing and a runny nose, as well as allergic conjunctivitis, which includes watering and itchy eyes.[12] Also an initial tickle on the roof of the mouth or in the back of the throat may be experienced.

Also, depending on the season, the symptoms may be more severe and people may experience coughing, wheezing, and irritability. A few people even become depressed, lose their appetite, or have problems sleeping. Moreover, since the sinuses may also become congested, some people experience headaches.[13]

If both parents have had allergies in the past, there is a 66% chance for the individual to experience seasonal allergies, and the risk lowers to 60% if just one parent has had allergies. The immune system also has strong influence on seasonal allergies, because it reacts differently to diverse allergens like pollen. When an allergen enters the body of an individual that is predisposed to allergies, it triggers an immune reaction and the production of antibodies. These allergen antibodies migrate to mast cells lining the nose, eyes, and lungs. When an allergen drifts into the nose more than once, mast cells release a slew of chemicals or histamines that irritate and inflame the moist membranes lining the nose and produce the symptoms of an allergic reaction: scratchy throat, itching, sneezing and watery eyes. Some symptoms that differentiate allergies from a cold include:[14]

• No fever.
• Mucous secretions are runny and clear.
• Sneezes occurring in rapid and several sequences.
• Itchy throat, ears and nose.
• These symptoms usually last longer than 7–10 days.

Among seasonal allergies, there are some allergens that fuse together and produce a new type of allergy. For instance, grass pollen allergens cross-react with food allergy proteins in vegetables such as onion, lettuce, carrots, celery, and corn. Besides, the cousins of birch pollen allergens, like apples, grapes, peaches, celery, and apricots, produce severe itching in the ears and throat. The cypress pollen allergy brings a cross reactivity between diverse species like olive, privet, ash and Russian olive tree pollen allergens. In some rural areas, there is another form of seasonal grass allergy, combining airborne particles of pollen mixed with mold.[15] Recent research has suggested that humans might develop allergies as a defense to fight off parasites. According to Yale University Immunologist Dr Ruslan Medzhitov, protease allergens cleave the same sensor proteins that evolved to detect proteases produced by the parasitic worms.[16] Additionally, a new report on seasonal allergies called "Extreme allergies and Global Warming", have found that many allergy triggers are worsening due to climate change. 16 states in the United States were named as "Allergen Hotspots" for large increases in allergenic tree pollen if global warming pollution keeps increasing. Therefore, researchers on this report claimed that global warming is bad news for millions of asthmatics in the United States whose asthma attacks are triggered by seasonal allergies.[17] Indeed, seasonal allergies are one of the main triggers for asthma, along with colds or flu, cigarette smoke and exercise. In Canada, for example, up to 75% of asthmatics also have seasonal allergies.[18]

In 1952 basidiospores were described as being possible airborne allergens[22] and were linked to asthma in 1969.[23] Basidiospores are the dominant airborne fungal allergens. Fungal allergies are associated with seasonal asthma.[24][25] They are considered to be a major source of airborne allergens.[26] The basidospore family include mushrooms, rusts, smuts, brackets, and puffballs. The airborne spores from mushrooms reach levels comparable to those of mold and pollens. The levels of mushroom respiratory allergy are as high as 30 percent of those with allergic disorder, but it is believed to be less than 1 percent of food allergies.[27][28] Heavy rainfall (which increases fungal spore release) is associated with increased hospital admissions of children with asthma.[29] A study in New Zealand found that 22 percent of patients with respiratory allergic disorders tested positive for basidiospores allergies.[30] Mushroom spore allergies can cause either immediate allergic symptomatology or delayed allergic reactions. Those with asthma are more likely to have immediate allergic reactions and those with allergic rhinitis are more likely to have delayed allergic responses.[31] A study found that 27 percent of patients were allergic to basidiomycete mycelia extracts and 32 percent were allergic to basidiospore extracts, thus demonstrating the high incidence of fungal sensitisation in individuals with suspected allergies.[32] It has been found that of basidiomycete cap, mycelia, and spore extracts that spore extracts are the most reliable extract for diagnosing basidiomycete allergy.[33][34]

In Canada, 8% of children attending allergy clinics were found to be allergic to Ganoderma, a basidiospore.[35] Pleurotus ostreatus,[36] cladosporium,[37] and Calvatia cyathiformis are significant airborne spores.[26] Other significant fungal allergens include aspergillus and alternaria-penicillin families.[38] In India Fomes pectinatus is a predominant air-borne allergen affecting up to 22 percent of patients with respiratory allergies.[39] Some fungal air-borne allergens such as Coprinus comatus are associated with worsening of eczematous skin lesions.[40] Children who are born during autumn months (during fungal spore season) are more likely to develop asthmatic symptoms later in life.[41]

• Asthma
• Bioaerosol
• Eczema
• Eggshell skull
• Hypoallergenic
• Immunodiagnostics
• List of allergies
• Nose filter
• Oral allergy syndrome
• Toxin

• General information on allergy and allergens
• Allermatch — Sequence comparison to allergenic proteins
• SDAP — Structural database of allergenic proteins
• Allergome Database
• Allergen Nomenclature