by David Claus, Ph.D.
Recent evidence shows they just might. It's not only those containing spermicides that are potentially toxic to sperm - they all might be - at least to some degree.
Years of peer reviewed, published research has shown that most sexual lubricants can decrease sperm's mobility, making it more difficult to reach an egg (1), but now there's a fair amount of credible research suggesting that those same lubricants might actually be toxic to sperm (2).
Just about all of the top selling lubricant brands have been studied, and time after time, mobility, motility and viability of sperm were dramatically reduced after exposure to the lube. Even in small concentrations these lubes not only impeded sperm's ability to swim, but also decreased their ability to survive and/or caused possible damage to their chromosomes (3).
What is it about these lubricants that is actually harming sperm?
It might be their acidity. Ideally the best pH value environment for a healthy sperm is between 7.0 and 8.5, or slightly alkaline. Lubricants tend to have pH values below 7, making most of them acidic. Some lubricants have pH values as low as 3 or 4. These overly acidic environments can cause sperm death. Actually, the vagina's own natural acidic secretions can even kill sperm. However, just before ovulation the pH of the cervical mucus rises slightly, which helps protect the sperm during this time.
Sperm are also sensitive to both high and low osmolality (concentration of osmotically active particles in solution) because these can cause the cells to either shrink or swell too much. A physiologic osmolality around 320 mOsm/kg (that of semen) is best for sperm function (4). Sperm motility decreases with exposure to increasing osmolality, with all motion stopping at 600 mOsm or greater. Lubricants have osmolality levels 3-10 times that of semen that causes irreversible damage to sperm motility. Even water based lubricants can contain glycerin (also potentially toxic to sperm) or propylene glycol, both of which are highly hyperosmotic.
Should you believe the marketing?
Many leading brands state in their marketing material that they "will not kill sperm" or that they have "no effect on sperm motility." This is in spite of published literature to the contrary. There are hundreds of personal lubricants on the market nowadays, offering everything from 'purely organic' versions to brands that contain spermicides, create heating sensations, or even include numbing agents. In our research, the 'Pure,' 'Natural' or 'Organic' versions fare no better than the others. If you are trying to conceive, one lube called Pre Seed claims to be completely 'sperm friendly,' and appears to have the actual data to back it up (5).