Learn It, Know It: Osmolality, AKA Lube Science

This post originally appeared on a previous iteration of this site on October 14th, 2014. It has been reposted here for posterity. 

There is a lot of misinformation out there about lubricants. I still hear people telling me silicone lube is not latex condom safe, That glycerine is a sugar that causes yeast infections2, and I could sit here and give you examples of lube misinformation for days, but I’ll spare you. The point is, there’s a lot of it floating around.

There are three common base-ingredients for lubricant: silicone, water, and oil. Today, I’m going to be talking about the water based- the most complicated, varied, and confusing of the bunch.

Now, I am no scientist. I’ve looked over information from people whom I trust and done a little bit of my own research to better understand the topic, and I understand this information to be true but admit that more research needs to be done in regards to personal lubricants and their interactions with the human body. That’s why I think this is important to talk about. 

Ok so, time for the science:

Molality is defined as the amount of substance (measured in mol) of solute, divided by the mass (in kg) of solvent, (not the mass of the solution). In other words, it’s the measurement of the mass of the stuff that’s dissolved in a liquid.

Osmolality is a variation of molality that only takes into account solutes that contribute to a solution’s osmotic pressure, and Osmotic Pressure in this instance is the measure of the tendency of a solution to take in water by osmosis.

Essentially, your orifices natural lubrication has a specific Osmolality- measured in milliOsmoles per killogram of solvent (mOsm/kg)- that your body is attuned to. When something of a different osmolality to what your body is accustomed to, specifically when it has a higher measure of mOsm/kg or is hyper-osmotic, the epithelial (surface) cells of your mucous membrane (in this case, the rectum or vagina) then expel the liquid they hold, drying up and actually sloughing off. This is kind of terrifying to think about, and also irritating to your skin while leaving you more susceptible to infection and contraction of an STI. Those cells sloughing off exposes underdeveloped cells to the outside world.

The Numbers

(courtesy of the Smitten Kitten’s really awesometastic “LUBE! An In Depth Look At Personal Lubricants” Brochure- I’ll include a list of their cited sources for these specific numbers below)

Mucous Membranes/Bodily Fluids Osmolality

Vaginal Mucus ~ 260-290 mOsm/kg (1)

Colon Lining ~ 920 mOsm/kg (2)

Human Semen ~ 260-380 mOsm/kg (1)

Common Lubricant Osmolality

Good Clean Love ~ 269 mOsm/kg (3)

K-Y Jelly ~ 2424 mOsm/kg (3)

ID Glide ~ 3429 mOsm/kg (3)

Astroglyde ~ 6113 mOsm/kg (3)

K-Y Warming Jelly ~ 10,300 mOsm/kg (4)

Slippery Stuff Liquid ~ 26 mOsm/kg (3)

Sliquid Organics ~ 106 mOsm/kg (3)

Tap water is about 3 mOsm/kg- in case you were wondering. Was I the only person that cringed at K-Y Warming Jelly? Because… yikes.

When a lubricant has a significantly lower measure of mOsm/kg, or is hypo-osmotic, the cells actually absorb the excess liquid. This could potentially lead to them bursting if they take in too much liquid- this seems less likely, since vaginal mucous osmolality is relatively low. When you look at the hyper-osmotic lubricants below, they are many many times more osmotic than vaginal mucous while there are no hypo-osmotic lubricants amongst the numbers I have. While Good Clean Love is hypo-osmotic to colon lining, it is not as significantly hypo-osmotic as many lubricants are hyper-osmotic to the vaginal lining.

The ideal is to have a lubricant that is iso-osmotic, or equally if not very close to the osmolality of your natural lubrication so there is little or no osmosis triggered in the cells inhabiting the epithelial layer of skin in your mucous membranes, in this case the vagina and rectum.

A good way to visualize this is a balance- when something is hypo-osmotic, it gives water to the cells lining the mucous membrane. When something is hyper-osmotic, it takes water from the cells lining the mucous membrane. The ideal is for there to be little or no need to create equilibrium, with equal levels of osmolality in both the cells and the lubricant, resulting in little or no exchange of liquids. What I’d like to know, though, are the numbers at which hyper- and hypo-osmotic lubricants become dangerous (i.e. trigger sloughing off or cell bursting) for the epithelial layer in the vagina and colon. Unfortunately, I don’t have those numbers- again, more research is needed and if I ever hear of research that clarifies this, I’ll be sure to post it here.

What kind of terrifies me about this whole thing is that yes, the FDA is currently testing personal lubricants- but I’ve found a PDF from www.accessdata.fda.gov (dated for what looks like…. June 21st, 1996?), the Summary For Safety and Effectiveness of K-Y Liquid. Although I don’t have a measurement for the osmolality of this specific lubricant, I think we can infer that it’s likely hyperosmotic, based on the measurements of the two other K-Y products. I could be wrong. Either way, in the tests that the FDA did- both in a “Clinical Dermal Irritation Study- Human Repeat Insult Patch Test” and a “10-Day Rabbit Vaginal Irritation Study with K-Y Liquid Personal Lubricant” they found that no humans were irritated or showed allergic reaction to either this or Astroglyde, and they did “not exhibit the potential to produce significant [emphasis mine] irritation in rabbits when administered intravaginally for ten consecutive days.”

First off, let me just feel bad for those rabbits for a moment.

Secondly, let me get mad about this. I’m mad because first, they don’t indicate where the dermal testing on humans was done, but I imagine that the specification of intravaginal for the rabbits means that it wasn’t intravaginal for the humans- which, in my eyes, renders the test void. Human skin is not the same in orifices as it is on other parts of the body, but of course my opinions don’t matter to the FDA. I will note that therewas consumer home testing mentioned in the report with those involved trying both Astroglyde and K-Y Liquid- but the only reported findings were that women did not prefer one more than the other.

The other reason I’m side-eyeing this is that  a significant amount of people have come to me with concerns about severe irritation from both K-Y and Astroglyde. All I’m saying is, the FDA seems more concerned with finding whether or not the claims made on the packaging of a product are true or not- in this case, they did testing to see how stain-resistant it was and noted that most of K-Y liquid’s ingredients were Generally Recognized As Safe, with the exception of one- Hydroxethyl Cellulose- which they note “has been safely used in the predicate device, K-Y- Jelly, for many years” -color me impressed (that’s sarcasm).

In the meantime, there’s only so much information available about Osmolality in lubricants. I know that the Smitten Kitten pamphlet was really intensely researched (for which I am very grateful) so I’m sure this is all that’s available in terms of Osmolality measurements of personal lubricants. I also know that Good Clean Love is one of the only companies (that I’ve seen) talk specifically about osmolality- it’s was mentioned in some marketing pamphlets I got from them awhile back. That’s probably why the Osmolality of their product is pretty much right on the money in relation to vaginal mucous. Sliquid isn’t terribly far off, either. Good on you, Sliquid.

I wanted to thank The Smitten Kitten yet again for making a really awesome guide to water based lubes- I was really lucky to get one at Woodhull Sexual Freedom Summit, where I got to meet the amazing founder and some of the awesome people that work there. The Smitten Kitten is really fantastic for a variety of reasons and makes me wonder if I should just move to Minneapolis- if you ever get the chance to visit, bring me with you. They were really what inspired the post, although I had read about Osmolality in Good Clean Love’s marketing materials about a year ago now. If you’d like your own copy of Smitten Kitten’s Lube guide, you can call or email them- visit their website for contact info.

My conclusion? There’s lots of research that still needs to be done in terms of lubricants and how they actually interact with human orifices. What I do know is that this makes sense, and is something I definitely both want to talk more and think more about- and something I want more research on.

(1) Adriaens, Els et al., “Microbicide excipients can greatly increase susceptibility to genital herpes transmission in the mouse.” BMC infectious diseases 10.1 (2010): 331

(2) Bakhshi, Rahul P. et al., “Hyperosmolar Sexual Lubricant Causes Epithelial Damage in the Distal Colon: Potential Implication for HIV Transmission.” The Journal for Infection Disease. 195 (2007):703-710. Web.

(3) Ayudhya, Kunjara Na, et al., “Is Wetter BetteR? An Evaluation of Over-the-Counter Personal Lubricants for Safety and Anti-HIV-1 Activity.” PLOS ONE.7 (2012):1-14. Web.

(4) Moench, Thomas R., et al. “Microbicide excipients can greatly increase susceptibility to genital herpes transmission in the mouse.” BMC infectious diseases 10.1 (2012):331.