Lubricant Osmolality

Water-Based Lubricants & Your Health

Lubricant Osmolality

Osmolality describes how concentrated a water-based lubricant is. Because highly concentrated lubes can cause irritation, promote infection, and impact fertility, we think osmolality is one of the most important things to know about your water-based lubricant. Here’s how to find safer, low-osmolality formulas.

What is Osmolality?

Osmolality measures the concentration of particles in a solution. Think of Kool-Aid. The water is the solvent and the drink mix is the particles, or solute. You can make a weak batch of Kool-Aid or a strong one.

Osmolality is measured as milliosmoles (solutes) per kilogram of water – abbreviated mOsmol/kg.

Our body fluids are relatively dilute – their osmolality ranges between 250 – 380 mOsmol/kg.

Osmotic pressure is created when the concentration of particles within a cell is different than the fluid surrounding it. Osmosis describes water moving into or out of a cell to balance the concentrations.

The Ideal Osmolality

Our mouths, vaginas, and rectums are lined with mucous membranes – a thin layer of epithelial cells & connective tissue called mucosa. This lining protects our body openings from pathogens, dirt, and dehydration.

Mucosa is thinner, more permeable, and provides more direct access to our blood stream than the skin covering our outer bodies. This is why some drugs can be taken under the tongue. It’s also why penetrative sex carries more risk than a handshake.

When it comes to lubricants & osmolality, we’re concerned with how concentrated a formula is relative to the fluids in & around our vaginal & rectal mucosa.

A lubricant that’s less concentrated than our body fluids is called hypotomic. In this case, more water will enter cells than leave. A small amount of water can be rejuvenating; too much and cells can burst.

While it would be great news for women struggling with vaginal dryness, there are very few lubricants that are hypotonic.

When a lubricant has a similar concentration as our body fluids, the lube is isotonic – it doesn’t create osmotic pressure and an equal amount of water moves into and out of skin cells.

Isotonic or near-isotonic lubricants are ideal for vaginal & rectal health and are usually marketed as ‘low-osmolality’.

A lubricant that’s more concentrated than our body fluids is hypertonic. In this case, more water will leave cells than enter. Too much water leaving a cell can damage or kill it. Unfortunately, most water based lubricants are highly concentrated.

The Osmolality of Water-Based Lubricants

And why it matters

Ideally a water-based lubricant for vaginal sex should have an osmolality of 260-290 mOsm/kg. A lubricant for anal sex should be 280-300 mOsm/kg. And a lubricant for women trying to conceive should be 250-380 mOsm/kg.

Unfortunately, most water-based lubricants are several times more concentrated than the ideals above. In fact, there are so few low-osmolality lubricants that the World Health Organization needed to relax their recommendations up to 1200 mOsm/kg.

In-vitro studies confirm that high-osmolality lubricants can damage vaginal and rectal tissues, cause irritation, and increase your risk of infection. High-osmolality lubricants can also damage sperm and impact your chances of conceiving.

1st Ingredient2nd Ingredient3rd Ingredient
Sliquid Organics Natural106Aloe VeraPlant CelluloseTocopherols (Vitamin E)
Genneve Water-Based250WaterPropanediolGluconolactone
Good Clean Love Almost Naked269Aloe VeraXanthan GumAgar
Divine 9700WaterCarrageenanPropylene Glycol
KY Jelly2,510WaterGlycerinHydroxyethylcellulose
Gun Oil H2O3,955WaterPropylene GlycolHydroxyethylcellulose
O'My Natural Lubricant4,348WaterGlycerinHydroxyethylcellulose
Astroglide Liquid8,064WaterGlycerinPropylene Glycol

How to Spot Low Osmolality Formulas

The short answer is to check out our reviews or look for premium formulas that specifically say ‘low osmolality’.

A lube’s formula is proprietary and osmolality is not disclosed on most FDA 501(k) summaries – the exception being lubricants sold as fertility-friendly.

Aside from expensive laboratory testing, the only way to determine a lube’s osmolality is if the manufacturer volunteers this information. Most manufactures aren’t forthcoming about the osmolality of their products, but a lubricant’s ingredients can provide clues.

Most water-based lubricants are water-glycol formulas and the strongest predictor of osmolality is glycol content. This means glycerin and propylene glycol based lubricants are the most likely to be highly concentrated and to cause problems.

Propanediol is also a glycol, but it’s a premium ingredient usually associated with gentler formulas.

While osmolality is of special concern for people who are prone to irritation or at risk of infection, and for women trying to conceive, we believe every vagina & rectum is sensitive. We strongly recommend avoiding glycerin-based lubes because of their high osmolality and because they’re notoriously sticky.

It’s important to stress that individual ingredients are only part of the picture. How much and in what combination are just as important. It’s completely possible to have a low osmolality formula that contains glycols. These formulas fall on the premium end of the spectrum, so expect to pay a little more.

Low Osmolality Lubricants We Recommend

Lubricants for Women Who are TTC


Considering how important it is to vaginal health, rectal health, and fertility, we find it hard to believe that osmolality is not required by the FDA or on product labels. And we find it frustrating that the industry doesn’t do more to regulate itself and promote the safest sex possible. Arghh!

In real life, it’s unclear at what point osmolality becomes a problem – how much of and how often a lubricant is applied certainly plays a role. But it makes sense to use products that either mimic nature or won’t disrupt natural processes.

Request information – Most manufacturers have websites and contact forms that make it easy to request product information (we use them all the time). You may not get the info you’re after, but you’ll be adding to the overall demand which can help push the industry in a better direction.

Low osmolality reviews – SLICK.SEXY tags a water-based lubricant as low osmolality when its concentration is known or can be reasonably estimated to be below 700 mOsmol/kg.

Water-glycol formulas – When choosing between propanediol, propylene glycol, and glycerin, go for propanediol and avoid glycerin.

Non-glycol formulas – Look for water and aloe-based lubricants that replace glycols with carrageenan and plant gums like xanthan and guar.

Plant oil lubricants – Osmolality doesn’t apply to plant oils. Check out our plant oil safety and DIY article here. If you’re not into DIY, check out our reviews and look for formulas that contain cold-pressed carrier oils like coconut, sweet almond, hemp seed, and grape seed – all of which have proven skin-loving qualities.

Silicone lubricants – Osmolality doesn’t apply to silicone lubricants. Silicones are inert, cannot be absorbed, and don’t require preservatives. From an ingredient perspective, they don’t contain anything to cause irritation. The best formulas are super slick, non-greasy, and don’t cling, so they won’t promote yeast infections or BV.

If you only have one lubricant on your nightstand, SLICK.SEXY recommends silicon for its safety, value, and effectiveness.

Our mission is to help you find better, safer lubricants – we hope this helps! Have you ever had a problem with a lube? Did you track the problem back to a specific ingredient? What do you look for instead? Let us know in the comments below ?


World Health Organization, United Nations Population Fund, & Family Health International. (2012). Use and procurement of additional lubricants for male and female condoms: WHO/UNFPA/FHI360 Advisory note. Retrieved from
Cunha, A. R., Machado, R. M., Palmeira-de-Oliveira, A., Martinez-de-Oliveira, J., das Neves, J., & Palmeira-de-Oliveira, R. (2014). Characterization of Commercially Available Vaginal Lubricants: A Safety Perspective. Pharmaceutics, 6(3), 530–542.
Edwards, D., & Panay, N. (2016). Treating vulvovaginal atrophy/genitourinary syndrome of menopause: how important is vaginal lubricant and moisturizer composition? Climacteric, 19(2), 151–161.
Vishwanathan, S. A., Morris, M. R., Wolitski, R. J., Luo, W., Rose, C. E., Blau, D. M., … Kersh, E. N. (2015). Rectal Application of a Highly Osmolar Personal Lubricant in a Macaque Model Induces Acute Cytotoxicity but Does Not Increase Risk of SHIV Infection. PLoS ONE, 10(4).
Adriaens, E., & Remon, J. P. (2008). Mucosal irritation potential of personal lubricants relates to product osmolality as detected by the slug mucosal irritation assay. Sexually Transmitted Diseases, 35(5), 512–516.
Dezzutti, C. S., Brown, E. R., Moncla, B., Russo, J., Cost, M., Wang, L., … Rohan, L. C. (2012). Is Wetter Better? An Evaluation of Over-the-Counter Personal Lubricants for Safety and Anti-HIV-1 Activity. PLOS ONE, 7(11), e48328.
Fuchs, E. J., Lee, L. A., Torbenson, M. S., Parsons, T. L., Bakshi, R. P., Guidos, A. M., … Hendrix, C. W. (2007). Hyperosmolar Sexual Lubricant Causes Epithelial Damage in the Distal Colon: Potential Implication for HIV Transmission. The Journal of Infectious Diseases, 195(5), 703–710.
Moench, T. R., Mumper, R. J., Hoen, T. E., Sun, M., & Cone, R. A. (2010). Microbicide excipients can greatly increase susceptibility to genital herpes transmission in the mouse. BMC Infectious Diseases, 10, 331.
Wolf, L. K. (2012). Studies Raise Questions About Safety Of Personal Lubricants. Chemical & Engineering News, 90(50). Retrieved from

Post Comment

Your email address will not be visible to others or sold to 3rd parties.