Background: Men who have sex with men (MSM) are at high risk for HIV acquisition and transmission. There is a high HIV-transmission potential associated with unprotected anal intercourse (UAI), which requires sexual lubrication for comfortable, non-traumatic anal sex. Lubricant distribution remains poor in many developing nations and MSM have been known to substitute a number of common household or food products to ensure comfortable anal sex. Concern has been raised about the potential toxicity of lubricants used during anal sex. Epithelial injury is related to the osmolality of the lubricant product., Objective: To analyse commercially available water-based sexual lubricant products to ascertain their osmolality and potential to cause rectal epithelial damage., Methods: The osmolality and glycerol concentration was determined for eight of the most frequently purchased water-based sexual lubricants and some commonly used household/food products., Results: Osmolality ranged from 270 - 9 440 mosmol/l (Lubrimaxxx Premium, containing phytosqualane, and JO H(2)O Water Based Lubricant, respectively). Seven (88%) of the commercial lubricants had high osmolalities, with two products approaching 10 000 mosmol/l, far in excess of serum which has an osmolality of ~280 mosmol/l., Conclusion: The results of this study show that many of the top-selling brands of water-based sexual lubricants available in SA are hyperosmolar. Given that hyperosmolar products have been shown in vitro and in vivo to cause epithelial injury, they may have the potential to increase HIV acquisition and transmission, if they are used during UAI. Awareness needs to be raised about the mucosal safety of lubricants designed for use during anal sex.