An evaluation of 13 sexual lubricants has found that, while many are toxic to the cells that line the vagina and rectum, this does not lead to an increased rate of HIV infection – at least in test-tube experiments.
The researchers conclude that, while some of these commercially-available compounds do cause damage to the epithelium, the layer of cells that line the vagina and rectum, this may not in itself be sufficient to increase the likelihood of HIV infection. This means that although the ‘lubes’ that cause the most damage to cells are in the main water-based ones, they are unlikely to reduce the efficacy of the condoms they are designed to be used with. Some other water-based lubes, and the silicone-based ones, were not toxic to cells.
The researchers confirmed that the main reason some lubes kill off tissue is because they contain more dissolved salts and other chemicals than the fluid inside cells: to use the technical term, they are hyperosmolar. This property means that they draw water out of the mucous membrane cells, drying them out and stripping them from the membrane surface. Two lubes tested were hypo-osmolar, meaning that instead the cells drew water out of the lube, which makes them swell and burst; one of these gels was toxic to cells too.
In contrast, the two gels that were iso-osmolar, meaning with the same fluid/salt balance as body fluids, did not damage mucous membranes; nor did the two lubes that were silicone- rather than water-based, and one of the hypo-osmolar ones.
While this property, osmolality, was the one most strongly associated with toxicity, preservatives found in some of the lubes were also toxic to cells, principally the compound chlorhexidine. This included KY jelly, probably the most long-established lube and one that has been used as a ‘control’ in some microbicide trials. Chlorhexidine, and possibly other preservatives, also killed off some beneficial vaginal bacterial (Lactobacillus species) that guard against bacterial vaginosis and may protect against HIV infection.
Alarmingly, it found that the two lubes it tested that were oil-based – and specifically aimed at gay men who choose not to use condoms – were also likely to cause rectal membrane damage.
In the experiments, lubes did not prevent infection, but they also did not amplify infection – in other words infected cells did not produce copies of HIV any faster than usual. This means that another process, such as active inflammation, may need to be there in order to increase the chance that a temporary, local infection of cells turns into a systemic, continuing one.
The research also found that cervicovaginal tissue was – contrary to what had previously been thought – just as likely to be damaged by some of the lubricants as rectal tissue.
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