What term describes a substance that prevents or relieves itching?

The term that describes a substance that prevents or relieves itching is "antipruritic." This is derived from the prefix "anti-" meaning against, and "pruritus," which is the medical term for itching. Antipruritics are specifically formulated to soothe the skin, alleviating discomfort associated with itching due to various conditions such as allergies, insect bites, or skin irritations.

On the other hand, antipyretic agents are used to reduce fever, not itching. Antimicrobial substances work against infection by killing or inhibiting the growth of microorganisms, which does not directly address itching. Antihistamines, though they can help alleviate itching in cases related to allergic reactions by blocking histamine (a chemical involved in allergic responses), are not exclusively classified as antipruritics. Therefore, the most precise term for a substance that treats itching is indeed "antipruritic."