Allergens: what they are, their list, and what can cause allergies

Allergens are substances that do not cause reactions in most people but trigger an immune system response in sensitive individuals. Below: what they are, which groups of allergens exist, and how the culprit is identified.

What allergens are and how they affect the immune system

An allergen is an antigen that causes allergic reactions in people sensitive to it. From a scientific standpoint, this is a type I hypersensitivity reaction mediated by the immunoglobulin E (IgE) response — as happens, for example, in atopic dermatitis.

Normally the immune system fights microbes, but in allergy it responds to a false alarm. Genes and the environment play a role. Antibodies migrate to mast cells covering the nose, eyes, and lungs, and upon repeated exposure to the allergen they release histamine — which irritates and inflames the mucosa. Hence the itching in the throat, sneezing, and watery eyes. Symptoms appear within minutes or after several hours.

What can cause allergies: the main groups of allergens

The common culprits are familiar to almost everyone:

• tree and grass pollen — seasonal pollinosis;
• dust mites and mold spores in household dust;
• fur, dander, and saliva of animals, most often cats and dogs;
• foods — peanuts, milk, eggs;
• bee and wasp stings, certain medications.

By origin, allergens are divided into household, epidermal, insect, pollen, food, drug, fungal, and helminth allergens. Pollen allergy is tied to the calendar: oak, elm, maple, birch, and alder bloom in spring, grasses in summer. Hence the question "what can cause allergies right now" — it is about the season.

Main food allergens: which lists exist

There is no single list of food allergens: official lists differ across countries — due to genetics and dietary habits. In the US, eight foods are recognized: peanuts, tree nuts, eggs, milk, shellfish, fish, wheat, and soy, as well as sulfites from 10 parts per million. Canada adds sesame and mustard, the European Union adds other gluten-containing grains, celery, and lupin.

Food allergy is not as common as food sensitivity. A reaction is caused by any form of direct contact: ingestion, inhalation, or touch.

Household, pollen, and contact allergens

Household — house dust, chalk and its solution in water, petroleum products. Epidermal — fur, down, feathers, dander, excrement, and saliva of cats, dogs, rodents, birds, and horses. Insect — micro-mites, cockroaches, stinging insects, arachnids.

Fungal — mold and yeast fungi, the main component of house dust, as well as basidiospores. Respiratory allergy to fungi is noted in 30% of people with an allergic disorder and in less than 1% with food allergy.

Contact: urushiol from poison ivy and poison oak causes contact dermatitis, while wood, paper, cardboard, MDF, and sawdust cause symptoms ranging from mild to severe, including asthma and rash.

How the allergen is identified: an overview of diagnosis

If you suspect an allergy in yourself or your child, the doctor may order testing or refer you to an allergy center. Options: a skin test — a small amount of allergen is applied to the skin and the reaction is observed; blood tests; a special diet with a gradual increase in the amount of the product. The doctor decides what to evaluate based on symptoms.

When to see a doctor

A reason for consultation is suspected allergy in you or your child. Symptoms: runny nose and sneezing, red or watery eyes, pain around the cheeks, eyes, or forehead, cough, wheezing, shortness of breath, hives, itching and redness of the skin, diarrhea, cramps and bloating, nausea, swelling of the eyes, lips, mouth, or throat.

Details help distinguish seasonal allergy from a cold: no fever, discharge is liquid and clear, sneezing is rapid and several times in a row, itching in the throat, ears, and nose, symptoms last longer than 7–10 days. Heredity: if both parents have allergies, the probability for the child is 66%; if one parent, 60%.

An allergic reaction in itself is not a reason to call an ambulance; 103 or 112 — if the lips, mouth, throat, or tongue suddenly swell, breathing is very rapid or you are gasping for air, the throat tightens and swallowing is difficult, the skin, tongue, or lips turn blue, gray, or pale, you suddenly become confused, drowsy, or dizzy, a person has fainted and does not wake up, a child has gone limp and is not responding as usual.

This material is for reference: it helps you navigate the topic but does not replace a doctor's consultation — it is calmer to sort out allergens together with an allergist.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer