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Best Water-Based Lubricants –

Use chemistry to pick the safest and most comfortable water-based lubricant for you and your Valentine

By Julianne Simpson, PT, DPT


Happy Valentine’s Day! You and your valentine may use lubricant during intercourse to increase glide and comfort or to decrease the risk of a condom breaking. There are three main types of lubricants on the market: water-based, silicone, and oil based. (Side note – oil can make condoms break. Don’t use oil with condoms!). This blog post focuses on water-based lubricants.

There is a wide array of lubricants on the market of varying quality and comfort. How on earth do you select the best lubricant? As a pelvic physical therapist, I use water-based lubricants for exams and treatment and have turned to chemistry to help me select the best and safest lubricants for my patients.

Two main chemistry factors play into lubricant’s ability to work well with your body: osmolality and pH. I will discuss osmolality first. Osmolality has to do with water crossing membranes and molecules dissolved in that water. A higher osmolality fluid has more solutes dissolved in it. If you are thinking of a cup of muddy water, a darker, muddier cup has higher osmolality than a cup of clearer water with just a small amount of mud in it. In the blue image, the drop on the left has higher osmolality. Osmolality governs the movement of fluids across a membrane. If the amount of solutes is the same on either side of a membrane, fluids won’t cross the membrane. We don’t want water to leave the cells of the epithelium (the top layer of tissues) in the vagina or rectum.

If a lubricant is hypo-osmolar, it causes water to move into cells which could cause bursting. If it is hyper-osmolar, it causes water to leave cells and can reduce the size of individual cells and therefore reduce the thickness of protective membranes in our vagina or rectum. If a lubricant is iso-osmolar, no fluid will cross cell walls. Ideally, lubricants would be iso-osmolar. See image with pink cells to illustrate osmolality.

Hypo osmolar lubricants can cause cells to swell and possibly burst.
Aaah isoosmolar lubricant. Fluids stay where they should.

If your lubricant’s osmolality does not match the osmolality of the tissues that it will be touching, skin irritation, burning, or micro trauma can occur. Vaginal, rectal and semen osmolality is about ~300 mOsm/kg, so ideally lubricants match this. The problem is that a LOT of the most common commercially available lubricants are hyper-osmolar which can cause disruption of the protective membranes inside our vaginas or rectums. See here for a list of lubricants with osmolality (and pH).

Going back to high school chemistry, pH is a measure of how acidic or basic something is. A low number means more acidic, a high number is more basic. The range is 0 to 14 with 7 being neutral. The pH in the vagina and rectum aid in

Hyper osmolar lubes cause water to leave cells and can damage our protective layer.

maintaining the microflora colonies which are critical for vaginal or rectal health. The microflora live best in a consistent pH. For the vagina, this is between 3.5 to 4.5. (slightly acidic). This rises to 6-7 post-menopausally. For the rectum this is ~7 (neutral). This means that it may make sense to use a different lubricant for vaginal vs rectal use.

So which lubes are the best? You can find tables on the web with several commercially available lubricants on Women’s Voices. For vaginal use, my current choice, what I use in the clinic, is Good Clean Love’s Almost Naked. For rectal use Yes But is my current favorite. Osmolality and pH are appropriate for rectal use. Slippery Stuff is slightly hypo-osmolar (26) but pH (6.7) is good for rectal use.

Which lubes should I avoid? According to the WHO, anything with an osmolality of 380 or less is OK to use until more iso-osmolar lubes are available.5 This pamphlet by Smitten Kitten has great graphics to show visually where lubes fall in terms of osmolality and pH. Generally, avoid anything warming, anything with fragrance or flavor.

Remember – it is not normal to feel pain or discomfort during sex! If you are feeling pain or discomfort during sex, one of Movement System’s Pelvic Health Physical Therapists may be able to help. See our Physical Therapists in our South Lake Union/ Seattle, Mercer Island or Gig Harbor locations.

Enjoy your Valentine’s Day with safer and more comfortable lubes!


Julianne Simpson, PT, DPT, holds a BA from Oberlin College and a Doctorate of Physical Therapy from Eastern Washington University. A general orthopedic and pelvic health therapist, she is passionate about helping people move more and empowering her patients to live healthier lives. She dreams of raising kind children, cycling over the Alps and surfing in Alaska.



  1. Begay O, Jean-Pierre N, Abraham CJ, et al. Identification of personal lubricants that can cause rectal epithelial cell damage and enhance HIV type 1 replication in vitro. AIDS Res Hum Retroviruses. 2011;27(9):1019–1024. doi:10.1089/AID.2010.0252
  2. Cunha AR, Machado RM, Palmeira-de-Oliveira A, Martinez-de-Oliveira J, das Neves J, Palmeira-de-Oliveira R. Characterization of commercially available vaginal lubricants: a safety perspective. Pharmaceutics. 2014;6(3):530–542. Published 2014 Sep 22. doi:10.3390/pharmaceutics6030530
  3. Ayehunie S, Wang YY, Landry T, Bogojevic S, Cone RA. Hyperosmolal vaginal lubricants markedly reduce epithelial barrier properties in a three-dimensional vaginal epithelium model. Toxicol Rep. 2017;5:134–140. Published 2017 Dec 16. doi:10.1016/j.toxrep.2017.12.011
  6. All images except photographs come from here.




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