Your skin is surprisingly resistant to a wide variety of assaults, but it's still susceptible to various invaders. Viruses, parasites, fungi, heat, and medications can all cause skin rashes and eruptions. Though not life-threatening, rashes are often bothersome, uncomfortable, or even painful. Some, such as heat rash and swimmers' itch, clear up on their own, while others, including rosacea and drug rashes, require medical treatment. Seek treatment when a rash is uncomfortable, painful, or persists for a long period.