Final answer:
A topical corticosteroid acts as a vasoconstrictor by constricting blood vessels in the skin, reducing inflammation and itching.
Step-by-step explanation:
A topical corticosteroid is a medication that is applied externally to the skin to treat various skin conditions such as inflammation, itching, and rashes. One of the methods of action of a topical corticosteroid is as a vasoconstrictor. This means that it constricts the blood vessels in the skin, reducing inflammation and itching.