Water Temperature for Washing, Explained: What a 50-Volunteer Hot vs. Cold Immersion Study Measured, and Why Lukewarm Is the Default Advice
Almost every cleansing guide says to use lukewarm water, and almost none say what they are comparing it with. A 2022 study from the University of Granada put numbers on the question: fifty healthy adults held one hand in hot water and the other in cold water, and researchers measured what happened to the skin barrier afterward. This guide covers what was measured, what it can and cannot tell you about washing your face, and where water temperature sits in a routine.
What the study actually did
The paper, published in the Journal of Clinical Medicine, enrolled 50 healthy volunteers aged 18 to 65 (20 men, 30 women). Each person immersed the right hand in hot water, averaging about 41 °C, and the left hand in cold water, averaging about 11 °C, for 10 minutes. Instruments measured transepidermal water loss (TEWL), surface pH, redness and stratum corneum hydration on the palms before and after. Measurements were taken in a room held near 23 °C.
Hot water: the largest change in barrier loss
After the hot soak, TEWL rose from about 25.8 to 58.6 g per hour per square meter, more than double. Surface pH moved from 6.33 to 6.65 and the redness reading rose from 249 to 286 arbitrary units. TEWL is a measure of how much water escapes through the skin, so a higher number means the barrier was holding less in at that moment. The authors concluded that hot water was more harmful than cold.
Cold water was not neutral either
This is the detail that gets lost in the advice. Cold water raised TEWL too, from 25.8 to about 35.0, and raised pH to 6.62, though redness did not change. The authors link part of the effect to long, continuous water contact itself, which they describe as disrupting the lipid layers between skin cells and swelling the cells. Temperature then adds to it: they cite work showing that warmth moves water out of the stratum corneum faster. Water exposure has a cost at any temperature, and heat adds to it.
What the study cannot tell you about your face
Be careful with the leap from palms to cheeks. The test used hands, which have a thick stratum corneum, and a 10-minute soak, far longer than a 30-second cleanse. The authors list a limited sample size, short follow-up and exposure time as limitations, and they did not test lukewarm water at all. Their recommendation to use cold or lukewarm water is a reasoned extension of the data, and they call for further work on the best temperature range. Treat it as direction, not a measured optimum.
What dermatology guidance says
The American Academy of Dermatology advises dampening the face with lukewarm water, cleansing gently with fingertips, avoiding scrubbing, patting dry and washing no more than twice a day plus after sweating. The Granada authors also note that the American Contact Dermatitis Society recommends cold or lukewarm water for hand washing. The reasoning matches the lab result: heat strips surface oils and raises water loss. Our guide to how often to wash your face covers the frequency side of the same advice.
How temperature fits with the rest of a cleanse
Temperature is one of several variables that change what a wash does to the barrier. The cleanser matters at least as much, and cleanser pH and the acid mantle explains why a soap-based formula pushes surface pH further than a syndet. Your tap supply matters as well, as the hard water study shows. Duration is the part you control most easily: the paper notes that WHO hand-washing guidance runs 40 to 60 seconds, and a face wash needs no more than that.
Showers, steam and the end of the wash
The study measured immersion, not showers, so any claim about shower temperature is an inference. The same mechanism would apply to long, hot contact on the face, which is a reason many dermatologists suggest washing the face at the sink with a short rinse rather than letting hot shower water run over it. Afterward, pat dry and apply moisturizer while skin is still slightly damp, since a barrier that has just lost more water benefits from a humectant and an occlusive, as described in our barrier repair guide.
A short checklist
Use water that feels neutral on the inner wrist, not hot. Keep the wash short, use a gentle cleanser, pat dry and moisturize. If your skin stays red, stings or flares after every wash regardless of temperature, that is a question for a dermatologist rather than another product. This article is educational, not medical advice: patch-test any new product on a small area first, and consult a dermatologist about persistent skin problems.
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