Their experiments showed that the best way to treat a sting from a man o’ war is to rinse the wound with vinegar to remove any residual stingers or bits of tentacle left on the skin, and then immerse the wound in hot water—ideally at a temperature of 113 degrees F (45 degrees C)—for 45 minutes. A hot pack will substitute nicely for the hot water, as will a spray called Sting No More, which was developed to treat combat divers under a Department of Defense grant. Even a quick, 30-second wash of diluted vinegar will confer protective effects.