Now let’s look at what the research says about the osmolality of lube. In a 2016 study investigating the importance of vaginal lubricant and moisturizer composition in patients experiencing specific menopause symptoms, published in Climacteric, they stated:
"Greater osmolality of personal lubricants has been significantly correlated with increased potential to cause mucosal irritation and tissue damage in a slug mucosal irritation (SMI) assay. This assay is used as a sensitive measure of mucous membrane tolerance for vaginal microbicide products and carriers, and the degree of irritation in the assay can predict genital burning, heat, and itching in humans.
High osmolality of personal lubricants has also been associated with cytotoxicity. In a prospective comparative, in vitro study, incubating sperm with hyperosmolar lubricants… led to loss of motility and DNA integrity. Exposure to hyperosmolar lubricants has also been shown in vitro to damage epithelial cell lines, and cervical and colorectal explant cultures, and, when applied rectally in humans, hyperosmolar lubricants cause significant damage and denudation of the epithelium."
What does all of that mean? It means that higher osmolality can lead to issues with irritation and micro-fissures (teeny, tiny tears we can’t usually see) in the vagina and anus. It also means that if a couple wants to conceive, osmolality can damage sperm. FertiltySmarts does a great job of exploring this further in the article Best Fertility Lubricants.
Another study, published in the Journal of Infectious Diseases, found that high levels of osmolality were connected to, “induced epithelial damage and possibly increased HIV susceptibility raises,” meaning that the increased friction and wear and tear on your internal skin can lead to higher risk of exposure to infections like HIV and other STIs.
What lubricant ingredients should be avoided?
But what about the fact that osmolality isn’t only caused by glycerin? Is glycerin itself or other factors the reason to be concerned about the ingredients in our lubricants?
De-Andrea Blaylock-Johnson, a clinical social worker and sex therapist, explains the importance of understanding pH balance and how lube ingredients may impact it,
“Generally, healthy bodies naturally balance the pH in our bodies. The vagina is naturally acidic (ranging between 3.8 and even 5.5 can be considered healthy). Most lubricants with really good ingredients are naturally closer to a neutral pH (6.8), however, some other lubes can be very acidic (one brand tests at 4.8). Lube can cause an imbalance in the natural pH, which disrupts the levels of bacteria and fungi and can cause infections or make the skin more susceptible to injury. “
While studies like the one just mentioned do discuss other factors such as preservatives and pH levels of lubricants as additional factors, study after study keeps bringing us back to the downsides of glycerin. Research points us back to how glycerin comes into the mix (again from the Climacteric study) :
"Glycol concentration is the primary factor determining osmolality for the majority of personal lubricants.
Apart from their key role in osmolality and mucosal irritation, glycols have also shown adverse effects in animal and in vitro studies. Vaginal application of glycerol monolaurate, glycerine, propylene glycol and PEG-8 all significantly increased susceptibility to herpes simplex virus 2 (HSV-2) in a mouse model.
An over-the-counter personal lubricant containing propylene glycol, glycerine, and methylparaben has also been shown to kill Lactobacillus crispatus in vitro, which is the dominant bacterial species in the vaginal microbiome that helps maintain a healthy mucosal barrier and acidic pH.
Indeed, recent personal lubricant use is associated with incident bacterial vaginosis outbreaks…and this is thought to be related to the presence of glycerine and/or the microbicidal preservative chlorhexidine in the lubricant."
This translates to the fact that glycols (glycerin) can increase infections and decrease the healthy bacteria in our bodies. These statements tell us that additional additives, such as common preservatives, can also be detrimental when applied to the vagina or anus.
Blaylock-Johnson notes that osmolality can be caused by other factors as well,
“Other humectants like propylene glycol, urea, or lactic acid can cause irritation. Additionally, petrochemicals can dehydrate mucus, leaving the mucous membranes more susceptible to bacterial vaginosis, sexually transmitted infections, or HIV. Also, lube that includes microbicide (like spermicide) can cause further irritation.”
Why is glycerin used in lubricants?
But what about the articles that say that this is all a big overreaction to nothing, and that glycerin isn't anything to worry about? After reviewing a number of these articles I did find some of them citing studies that were inconclusive, but none that affirmed that glycerin was in fact safe. A number mentioned that glycerin is FDA safe for use in food and makeup products, but this does not mean that it isn’t causing potential damage when touching and being absorbed by vaginal and rectal tissues.
As much as personal experience and opinion matter, particularly if we are making statements about medical safety, it is important that we evaluate the sources that are putting the information forward. A number of pro-glycerin articles can be found on the websites of lube brands that use glycerin, so they may not necessarily be without bias. The gold standard is peer-reviewed research to support a position, which to date I could not find to support the benefits of glycerin in lube.
Read: What kind of lubricant should I use for anal sex?
Ultimately, glycerin should be used with caution because it is a sugar alcohol derived from animal products, plants, or petroleum. Vegetable glycerin is made with plant oils. And, in essence, glycerin is used to slow the growth of bacteria, which may affect all types of bacteria—healthy and unhealthy.
Family Nurse Practitioner and Halal Sexpert Dr. Shaakira Abdullah, points out there there are a number of other considerations when exploring your lube options. She shares,
"[there are] benefits of glycerol as well. For example, oil-based lubricants with glycerine tend to last longer than natural water-based products for users. However, in my opinion, the potential harm far outweighs this benefit. Water-based lubricants without harmful ingredients such as glycols are much more similar to natural lubrication system and better coincide with their natural flora system than oil-based lubricants."
Blaylock-Johnson avoids glycerin in lube, adding:
"Not everyone with a vulva who uses lube that contains glycerin will get a yeast infection, but if you are already prone to them, avoiding lube that contains glycerin would be the best option. Be sure to look for body-safe choices that clearly explain they are free from petrochemicals, glycerin, and parabens.”
At the end of the day, each person must decide what lubricants are, or are not, right for them. Glycerin in lube does have benefits- they stay wetter longer and that can increase pleasure and safety in many respects. But as conscious consumers, we must also be fully aware of what science tells us are cautions and considerations as well. The most important part of making any decision is knowing the facts, determining what research tells us, allowing us to feel empowered in whatever path we choose.