This red, itchy rash happens when an outside substance irritates your skin. Common culprits are chemicals in soap, cologne, detergent, or even spermicide. An outbreak usually develops within a few minutes to a couple of hours after contact. It’s not contagious, but can linger for up to a month. If you develop a rash, think of any new products you might have used recently. Stop using them to see if your symptoms improve.