Lubricants have an unquestionably sensual function: to make sex feel better. People use a wide variety of substances to increase their pleasure during sex and to eliminate pain. In the global response to HIV among MSM, lubricants also serve an important function in the prevention of HIV transmission. Appropriate lubrication reduces the likelihood of condoms tearing and it reduces physical damage to the rectal lining during anal sex. But proper lubrication is in short supply globally, and we know little about the effect of lubricants on the rectal lining.