From a biochemistry perspective, allergens are typically proteins or polypeptides that are found in certain foods, medications, or environmental substances such as pollen, dust mites, and animal dander. When a person is exposed to an allergen, their immune system produces specific antibodies known as immunoglobulin E (IgE) that bind to the allergen and trigger the release of histamine and other chemicals into the bloodstream. These chemicals cause the symptoms of an allergic reaction, which can range from mild (such as sneezing and itching) to severe (such as difficulty breathing and anaphylaxis).

Some common allergens include peanuts, tree nuts, shellfish, dairy, eggs, wheat, soy, and certain medications. Allergies can develop at any age and can be triggered by a variety of factors, including genetics, environmental exposures, and the presence of other allergies.

Diagnosing allergies usually involves a combination of medical history, physical examination, and allergy testing, which can include skin prick tests or blood tests to measure levels of specific IgE antibodies. Treatment options for allergies may include medications to relieve symptoms, allergen immunotherapy (also known as allergy shots), and lifestyle changes to avoid exposure to the allergen.

In summary, allergens are substances that can cause an allergic reaction in certain individuals by triggering an immune response. Understanding the biochemistry of allergens can help in the diagnosis and treatment of allergies and can also help individuals with allergies to manage their condition and avoid potential triggers.