Calamine lotion. If you're allergic to it like I am, oatmeal based rash lotions and baths work. So does vinegar. It stinks like hell, and will sting the irritated skin, but it neutralizes the histamine response in your skin and will clear up the rash, too. Plus, it works on "no see ums," and other biting pest stings, too.

u/inga is right, also. But you have to keep rinsing the wash cloth off after you scrub a part of your body, and work from the top down.