Allergen

An allergen is a substance that is usually harmless but can cause an allergic reaction in some people. It can trigger their immune response.

Our bodies use a special defense called immunoglobulin E, or IgE, to fight off parasites. But sometimes, people who are very sensitive make IgE even when there is no real danger. This can lead to a type-I hypersensitivity reaction.

Many different things can become allergens for different people. What causes a reaction in one person might not affect another. Groups like the World Health Organization and the International Union of Immunological Societies keep lists of substances that cause these reactions.

Examples

Allergens can come from many places, like tiny bugs called dust mite or certain foods. Some foods, such as peanuts (a type of legume), nuts, seafood, and shellfish, can cause serious reactions in many people.

Different places have different rules about which foods can cause allergies. For example, the United States Food and Drug Administration has a list of major food allergens. Other countries may have different lists based on what people commonly eat there.

Allergic reactions can happen in many ways: eating a food you're sensitive to, breathing in pollen or perfume, or even touching a plant that causes allergies. Stings from wasp, fire ant, and bee, as well as medicines like penicillin and materials like latex, can also trigger reactions. A very serious reaction is called anaphylaxis.

Sometimes, a person can have an allergic reaction the very first time they come into contact with something.

Non-IgE

Some substances can cause reactions that are not related to the usual allergy process. For example, a substance in poison ivy and poison oak can cause a rash on the skin.

Even everyday things like trees, paper, or wood products can sometimes cause reactions, like asthma or skin rashes.

Common

Main article: List of allergens

Allergens are things that can make some people have allergic reactions. Common allergens include:

• Animal things like cat allergy to cats, fur, dander, cockroach parts, wool, and dust mite bits.
• Drugs such as penicillin, sulfonamides, and salicylates found in many fruits.
• Foods like celery, corn, eggs, legumes such as beans and peas, peanuts, soybeans, milk, seafood, sesame, soy, tree nuts like pecans and almonds, and wheat.
• Insect stings from bee and wasp venom, and mosquito bites.
• Mold spores.
• Metals like nickel and chromium.
• Other things such as latex, wood, and plant pollens that can cause hay fever from grasses like ryegrass and timothy-grass, weeds like ragweed, and trees like birch.

Seasonal

Seasonal allergies happen at certain times of the year, like in spring, summer, or fall. This is when plants such as trees and grasses release pollen into the air. If someone is sensitive to this pollen, their body may react. They might sneeze, have a runny nose, itchy or watery eyes, and sometimes coughing or wheezing.

Doctors can help find out if someone has seasonal allergies. They look at the symptoms and may do tests. These tests could be a blood test or a skin test to see how the body reacts to specific allergens. Other tools, like looking at cells from the nose under a microscope, can also help confirm an allergy.

Fungal

Fungal spores from mushrooms, rusts, smuts, brackets, and puffballs can cause allergies, especially in people with asthma. These spores are in the air and can make breathing hard. Rainfall can make more spores appear, which may cause more asthma problems for children.

Treatments for fungal allergies include medicines you can buy without a prescription, such as antihistamines and nasal sprays. These can help with sneezing and a stuffy nose. Some newer medicines cause less sleepiness. Allergy shots are also an option. These shots slowly give small amounts of the allergen to help the body get used to it. For egg and milk allergies, some children can slowly eat small amounts of cooked foods under the care of a dietitian to build tolerance.