Water-Based Lubricant: Important Considerations for Vaginal and Anal Sex
Video-Related Articles

Water-Based Lubricant: Important Considerations for Vaginal and Anal Sex

What kind of lubricant you are using is important! Whether you are having vaginal sex, anal sex, or a combination of the two, if you are using lubrication we should talk about it!

This post focuses specifically on water-based lubricants because, as a human, your cells are made of at least 50% water if not more—thus, both your vagina and rectum reabsorb water-based lubricants. This isn’t inherently dangerous, but you should know what you are introducing into your body.

If you would rather watch than read, check out this video from my youtube channel!

As an aside, while water-based lubricant is reabsorbed by the body, it is the easiest lubricant to clean up! It will come right out of other materials in the wash! The other options, silicone-based or oil-based, tend to stain materials like sheets, couches, car seats, etc. Know that silicone-based lubricant will degrade silicone toys (in that silicone bonds to silicone, so your potentially expensive toys can turn into a sticky mess), and oil-based lubricant will degrade latex condoms (in that the condom material may become weak and break down)—and choose accordingly! I will expand on silicone- and oil-based lubricants in future articles, but for now, here is a handy chart.

A chart outlining the attributes of water-, silicone-, and oil-based lubricants.

When discussing water-based lubricants, it is important that we consider osmolality, pH levels, and ingredients. Let’s make sure osmolality and pH make sense and dive into why we should consider them as well as ingredients in our water-based lubricant decision-making!


In chemistry, a solution is a combination of a solute and a solvent, where the solute dissolves in the solvent. This is significantly easier to conceptualize if you think about salt water as a solution. That sentence restated then becomes: salt water is a combination of salt and water, where salt dissolves in water. Body fluid can also be viewed as a solution containing solutes (such as electrolytes) in a solvent (water).

Osmolality is the measure of solutes in a solution—or a fancy way of saying the amount of salt in salt water, or the amount of electrolytes in body fluid.

Why should you be thinking about chemistry when buying a lubricant? Because your cells will lose or gain water depending on the kind of lubricant you introduce into your body through a process called osmosis. Think about using salt to cure meat—someone would salt the meat to draw the water out of it. The same thing happens when you put salt on a slug. The slug would become shriveled, because water would exit its body and be pulled towards the salt. In the same vein, if a slug were to eat a lot of salt, and then go for a swim, water would enter the slugs body and make him swell. Water follows salt to try to create balance, or equilibrium.

An example of a slug shriveling due to osmosis.

If you introduce a lubricant into your vaginal or rectal canal that has more solute than the cells that line your canal, water will leave those cells and enter the lubricant to try to create a balanced concentration of solute (aka equilibrium)—just like salting a slug!

Some lubricants could have more solute concentration than your body (salting the slug), some lubricants could have the same as your body, and others could have less (the slug eating salt and going swimming). Those lubricants are referred to as “hyper-osmotic,” “iso-osmotic,” and “hypo-osmotic” respectively.

In theory, if a lubricant was hyper-osmotic, it would cause the cells in your vagina or rectum to lose water and dehydrate, if a lubricant was iso-osmotic, nothing would happen, and if lubricant was hypo-osmotic, it would cause the cells in your vagina or rectum to gain water, potentially causing hydration, or, if too much water entered, the cells could burst.

An example of hyper-osmotic lubricant, where solute leaves the body and dehydrates the body's cells. An example of iso-osmotic lubricant, where there is no osmosis.

An example of hypo-osmotic lubricant, where water leaves the lubricant and enters the body's cells, causing the cells to enlarge.

The osmolality of human plasma is around 300 mOsm/kg. (mOsm/kg is the proper unit to measure osmolality, its details are not important for our understanding). That means the anything more than 300 mOsm/kg would by hyper-osmotic, and anything less than 300 mOsm/kg would be hypo-osmotic.

A scale of osmolality, with your body's 300 mOsm/kg in the center.

The World Health Organization recommends that lubricants do not exceed more than 380 mOsm/kg; however, a lot of commercial lubricants exceed this value, so generally 1200 mOsm/kg is deemed acceptable1. Where are the most common brands of water-based lubricant on this scale?

Replens, KY, and Astroglide on the osmolality scale.

Replens: 2143 mOsm/kg (hyper-osmotic)

KY Jelly: 2463 mOsm/kg (hyper-osmotic)

Astroglide: 5848 mOsm/kg (very hyper-osmotic)

Remember our earlier slug analogy? A super cool study that uses a species of slugs whose mucosal lining is similar to the vaginal mucosal lining finds that “moderately hyper-osmotic” lubricants, like Replens and KY, cause “mild to moderate irritation,” and “very hyper-osmotic” lubricants, like Astroglide, cause severe irritation and tissue damage2.

A different study showed that hyper-osmotic lubricants, defined this time as >1000 mOsm/kg (which would include Replens, KY, and Astroglide), when applied rectally in humans, caused tissue damage and loss of the first layer of skin3.

All of this to say, while lubricants with osmolality values that are off the charts are usually the cheapest and easiest to purchase, I highly recommend sticking to lubricants that are iso-osmotic, or close reflections of our natural osmolality.

A chart of common lubricants and their osmolality, noting whether they are hyper-, iso-, or hypo-osmotic.

Another aside—if you are getting chronic vaginal yeast infections, check your lubricant! Hyper-osmotic lubricants can cause vaginal irritation (in the form of itchiness and redness), which can be misdiagnosed as yeast infections! 


pH is the measure of acidity and basicity in a water based solution. It is scaled 0—14, where 7 is considered neutral, <7 is acidic, and >7 is basic.

A pH scale with water in the center, with a pH of 7.

To better visualize that scale, compare the pH values of the following:

Vinegar: 2-3 pH

Vaginas: 3.8-4.5 oH

Water: 7 pH

Rectums: 7-8 pH

Milk of Magnesia: 10.5 pH

A pH scale detailing vinegar, vaginas, water, rectums, and milk of magnesia for comparison.

Vaginas are naturally more acidic, with a normal pH value ranging from 3.8-4.5, where rectums are more neutral, averaging a pH value of 7-84. Maintaining the normal pH value in both the vagina and rectum is important, because a change in the pH can foster the overgrowth of certain bacteria, leading to potential infection.

Since vaginal and rectal pH levels are different, one lubricant cannot serve as the optimal choice for both vaginal and anal sex! If you are participating in one, the other, or both, find the lubricant that matches the appropriate pH!

A chart detailing common lubricants and their osmolality as well as their pH, and whether the pH is vaginal- or anal-friendly.


Lubricants can contain a number of ingredients—I want to focus on the two that get the most attention: glycol and parabens.

Glycol is used not only to moisturize your skin, but also to reduce the loss of moisture in the lubricant. In other words, it keeps you and your lubricant wet. Its common forms are: glycolol, glycerin, and propylene glycol. Research shoes that glycol kills a particular bacteria that lives in the vaginal environment called lactobacillus crispatus. This bacteria is important because it is responsible for both a healthy mucosal barrier and the vagina’s acidic pH5! This may be why recent use of lubricant can be associated with new onset bacterial vaginosis—an infection caused by the overgrowth of bacteria in a vaginal environment whose pH is no longer acidic, but is instead too basic6. If you are having chronic bacterial vaginosis, check your lubricant!

The research on parabens, on the other hand, isn’t as strong. Lubricants use paragons as preservatives. We know that parabens have low levels of estrogen, they may interfere with our hormone system7-9, and they have been detected in breast tumors10; however, a direct correlation with cancer has yet to be established. That being said, why take the risk?

A chart detailing common lubricants and their osmolality, pH, and whether or not they contain glycol or parabens.

My charts are all adapted from this amazing open access article, check out their chart for a more comprehensive list of common lubricants and their osmolality, pH, and ingredients!

In Closing

When it comes to a lubricant, why not choose a lubricant that matches both your osmolality and pH levels, and stay away from ingredients that may kill off your good bacteria or cause cancer? Because no one talks about it!

My intention is not to steer you towards any specific product. Instead, I want you to have the knowledge necessary to make an informed decision when purchasing water-based lubricant, and a potential answer to redness and/or irritation related to vaginal and/or anal sex.

Happy shopping, and cheers to safe, healthy sexy-time! Stay tuned for more on silicone- and oil-based lubricants!

Are you looking for a pelvic provider in your area? Search for a pelvic physical therapist near you, here!


  1. Edwards D, Panay N. Treating vulvovaginal atrophy/genitourinary syndrome of menopause: how important is vaginal lubricant and moisturizer composition?. Climacteric. 2016;19(2):151-61.
  2. Adriaens E, Remon JP. Mucosal irritation potential of personal lubricants relates to product osmolality as detected by the slug mucosal irritation assay. Sex Transm Dis. 2008;35(5):512-6.
  3. Dezzutti CS, Brown ER, Moncla B, et al. Is wetter better? An evaluation of over-the-counter personal lubricants for safety and anti-HIV-1 activity. PLoS ONE. 2012;7(11):e48328.
  4. World Health Organization. Use and procurement of additional lubricants for male and female condoms. Available from: http://apps.who.int/iris/bitstream/10665/76580/1/WHO_RHR_12.33_eng.pdf
  5. Fashemi B, Delaney ML, Onderdonk AB, Fichorova RN. Effects of feminine hygiene products on the vaginal mucosal biome. Microb Ecol Health Dis. 2013;24
  6. Brotman RM, Ravel J, Cone RA, Zenilman JM. Rapid fluctuation of the vaginal microbiota measured by Gram stain analysis. Sex Transm Infect. 2010;86(4):297-302.
  7. Błędzka D, Gromadzińska J, Wąsowicz W. Parabens. From environmental studies to human health. Environ Int. 2014;67:27-42.
  8. Karpuzoglu E, Holladay SD, Gogal RM. Parabens: potential impact of low-affinity estrogen receptor binding chemicals on human health. J Toxicol Environ Health B Crit Rev. 2013;16(5):321-35.
  9. Nohynek GJ, Borgert CJ, Dietrich D, Rozman KK. Endocrine disruption: fact or urban legend?. Toxicol Lett. 2013;223(3):295-305.
  10. Harvey PW, Everett DJ. Significance of the detection of esters of p-hydroxybenzoic acid (parabens) in human breast tumours. J Appl Toxicol. 2004;24(1):1-4.


  • waqas sher

    thankyou, this article was very helpful i got my answers, we have chosen to buy YES products as they seem to be the only ones who care and have the correct products, hoping the shipment arrives in pakistan with no trouble.
    cheers & thanks again for caring.

    • pelvicempowerment

      I am so glad this was a helpful article for you! Yes, water-based lubricants I like include the YES products as well as Good Clean Love. That being said, my husband and I use coconut oil 🙂

      Wishing you and yours only the best, don’t hesitate to ask any other questions!

  • waqas sher

    i can see you have done your research and i am very thankful for the information you have given us, but if you don’t mind please give us some names of products that are the best for vagina that you have found as it would take us months to check all the products out there.

Leave a Reply

Your email address will not be published.