Heat Rash

How to Avoid It: Heat rash, also known as prickly heat, occurs when sweat becomes trapped under the skin. The tiny red bumps feel prickly and often itch, explains Ava Shamban, a dermatologist in Santa Monica. (The blockages also disrupt the cooling effects of sweating and can, in extreme conditions, contribute to heat exhaustion.) To prevent heat rash, use an exfoliant or a washcloth a couple of times a week in the shower to slough off dead skin cells, and try to stay cool and dry.

Once You’ve Got It: If you do develop heat rash, apply Sarna Lotion ($10, www.drugstore.com), a soothing lotion with camphor and menthol; or a 1 percent hydrocortisone cream. You can also take a lukewarm bath with a handful of colloidal (milled) oatmeal or a product that contains oatmeal, such as Aveeno Skin Relief Bath Treatment ($7 at drugstores). With treatment, the bumps should disappear in two to three days.