There has been a lot of discussion lately about the safety of personal lubricants, particularly during anal sex. The truth is, this is not a new controversy. Concerns about the relationship between lubricant use and HIV transmission first hit the news over a decade ago. That was when it was discovered that nonoxynol-9 didn't just disrupt the membranes of sperm cells, as it was designed to do, it disrupted the membranes of vaginal and rectal cells as well. However, these days the discussion is focusing on something different -- osmolality.
Osmolality refers to the amount of solutes, particles like salts and sugars, in a liquid or gel. Since cells naturally balance osmotic pressure, high osmolality lubricants can basically suck the moisture out of your skin cells,. This may make them more susceptible to damage, or even kill them outright. It is not surprising that there is, therefore, some information that use of hyperosmolar lubricants may increase the risk of STD transmission, particularly during anal intercourse.
That said, the risk of using a less than ideal lubricant for anal sex is still likely to be lower than that of not using a lubricant for anal sex - particularly if you use it along with a condom. Insufficiently lubricated sex can sometimes cause skin damage, even to the point of bleeding, which also increases the risk of getting an STD.