A counterirritant is a substance that is applied to the skin to cause a mild irritation (like tingling or cooling) in order to block a separate sensation of pain. Mentholated sports creams and rubs are a typical example of counterirritants. When you have muscle soreness or pain, these rubs cause a strong cooling or tingling effect on your skin. This signal is sent straight to the brain and travels faster than the pain signals from your sore muscles, thus crowding the pain signals off your nerve system's "highway" to your brain. This happens because your nervous system typically gives priority to signals coming from outside your body, i.e. on your skin which may represent an immediate danger - like being bitten by an animal or getting burned.