What term describes an immune response to usually harmless substances?

The term that describes an immune response to usually harmless substances is "allergy." Allergies occur when the immune system mistakenly identifies a typically innocuous substance, such as pollen, pet dander, or certain foods, as a threat. This triggers an exaggerated immune response that can result in symptoms like sneezing, itching, swelling, or more severe reactions.

Understanding allergies is crucial because they can affect hair and skin health. For instance, some individuals may have allergic reactions to certain hair products, leading to scalp irritation or contact dermatitis. Recognizing the triggers and understanding the nature of allergies can help beauty professionals make informed choices about products and techniques used in their practice to ensure the comfort and safety of clients.

The other terms in the choices represent different concepts. Alopecia refers to hair loss, amphoteric describes a substance that can react as either an acid or a base, and surfactants are compounds that reduce surface tension between liquids and are often used in cleaning and cosmetic products. None of these terms pertain directly to the immune response to harmless substances like allergies do.