What term refers to a reaction caused by extreme sensitivity to a normally harmless substance?

The term that refers to a reaction caused by extreme sensitivity to a normally harmless substance is "allergy." An allergy occurs when the immune system mistakenly identifies a harmless substance, such as pollen, certain foods, or pet dander, as a threat. In response, the body generates an immune reaction that can manifest in various symptoms, including sneezing, itching, hives, or even more severe responses like anaphylaxis.

This immune response can vary between individuals, explaining why some people react strongly to substances that others tolerate without any issues. Understanding allergies is crucial for estheticians, as they must be aware of potential allergens in skincare products and treatments that could affect clients. This knowledge helps in preventing adverse reactions and ensuring a safe and comfortable experience for clients receiving esthetic services.