allergen

Substances that are recognized as a threat by the immune system, leading to an overreaction, are known as allergens. These can be a variety of things, including pollen, dust mites, certain foods, or pet dander. The immune system's response to an allergen can cause symptoms such as sneezing, itching, and a runny nose. In severe cases, exposure to allergens can lead to anaphylaxis, a potentially life-threatening reaction.