Does Drinking Water Hydrate Your Skin? What a 49-Volunteer Trial of Two Extra Liters a Day Measured, and What a Six-Study Review Concluded

Where your daily water actually comes from

Before asking whether more water helps, it helps to know what "water intake" includes. In the 2015 trial from Lisbon, volunteers completed a food frequency questionnaire that counted three sources: drinking water, water inside food, and water produced by metabolism. In that group, drinking water made up only 32.4 percent of the total, food supplied 57.2 percent and metabolism 10.4 percent. For reference, the paper cites European Food Safety Authority reference values of 2.0 liters a day for women and 2.5 liters for men, counting water from both drinks and food.

The 2015 trial, step by step

Palma and colleagues recruited 49 healthy women aged 22 to 34 (mean 24.5). Using cluster analysis of the questionnaire, they split them into Group 1, with a total intake under 3,200 mL a day (38 women), and Group 2, above 3,200 mL (11 women). Everyone was then asked to add roughly 2,000 mL of water a day for 30 days. Measurements were taken at day 0, 15 and 30 on the face, forearm, hand and leg, using a capacitance-based moisture meter for surface and deeper hydration, a Tewameter for transepidermal water loss, and a Cutometer for mechanical properties.

What the trial measured

Skin hydration readings rose in both groups, but significantly more in Group 1, the lower drinkers, and in every body area tested. Transepidermal water loss, a measure of how quickly water leaves through the barrier, did not change meaningfully in either group. Some Cutometer values, such as extensibility, shifted as well. The authors concluded that higher water input might positively affect normal skin physiology, particularly in people who normally drink less.

Why the result needs careful reading

This was a convenience sample of young women, with no placebo or untreated comparison arm described in the design: every participant added water. Group 2 had only 11 people. Instruments measure hydration of the outer layer in arbitrary units, not how skin looks or feels, and a month is short. The study does not show that anyone's skin looked better, and it cannot separate water from other changes across the 30 days. It is a useful signal rather than a settled answer.

What the 2018 systematic review found

Akdeniz and colleagues at Charite in Berlin searched the literature on dietary fluid intake and skin hydration in healthy people. Of 216 records, 23 were read in full and only six studies were included, with mean participant ages between 24 and 56. Their summary: the evidence is weak in both quantity and methodological quality. A slight increase in stratum corneum and deeper skin hydration appeared after extra water, especially in people with lower prior consumption, and some studies saw small gains in extensibility and elasticity. They also noted a lack of evidence that drinking more water brings dermatological benefits.

Water inside versus water on top

Two different things are easy to blur. Drinking water supports the body's overall fluid balance. Whether the outer layer of skin holds water depends heavily on its own barrier and humectants, such as the compounds described in our natural moisturizing factor guide, and on the air around you, as covered in our piece on dry indoor air. Skin that feels tight is often described as dehydrated in the label sense, a topic our dry versus dehydrated skin explainer separates from low oil.

What a routine can do that a glass cannot

The research above measured one input. A routine has others you control directly. A humectant such as glycerin, covered in our glycerin explainer, binds water at the surface, and a sealing layer slows its loss. None of this replaces drinking when you are thirsty. It just means the glass is one small lever among several.

Practical takeaways

If you already drink to thirst and eat a varied diet, the evidence does not suggest forcing extra liters for your skin. If your intake is low, the small trials hint that adding some water may nudge surface hydration readings, which is a reasonable reason to drink more regardless. Persistent dryness, itching or flaking is a question for a dermatologist, not a hydration target.

This article is educational, not medical advice. Patch-test any new product on a small area first, and consult a dermatologist about persistent dryness, itching or rashes. Sources: Palma et al., Clinical, Cosmetic and Investigational Dermatology 2015;8:413-421; Akdeniz et al., Skin Research and Technology 2018 (systematic review of dietary fluid intake and skin hydration); checked October 2026.