Researchers at the University of Berlin took a look at studies published in peer-reviewed journals that examined an increase in water intake and measurements of skin hydration. On Pubmed and Web of Science they found 216 records. Many of those were duplicates, unrelated, or didn’t have enough data. From those 23 were selected, many were dropped due to a high risk of bias…leaving them with 6.

With these 6 studies, of which 5 were experimental, the mean age of the samples ranged from 24 to 56. So if you’re much younger or older than that – these conclusions may not apply to you.

The experiments showed a slight, but statistically significant, increase in stratum corneum hydration when people drank an extra 1 to 2 litres of water a day. The increase was more significant if people were consuming low amounts of water previous to the experiment.

There was no difference in measurements of trans-epidermal water (TEWL) loss in any of the studies. TEWL is often used as an analogue of the skin’s barrier permeability and is a measurement of the amount of water evaporating from the skin. A decrease in TEWL is usually seen as a decrease in permeability.

Other studies looked at skin smoothness, skin roughness, and skin elasticity. While some of the studies showed slight positive effects when consuming mineral water, other similar studies showed no effect.

A couple papers looked at the effect of consuming water on the skin’s pH. In one experiment they found men had a slight decrease in skin pH when consuming 100 mL of water. And the other experiment found a decrease in skin pH when consuming 2.25 L of tap water, but not mineral water.

The researchers point out that measurement devices using electrical capacitance to measure stratum corneum hydration can be affected by dermal hydration. So the readings might be off. As well they point out that the “logical” thought of increased dermal hydration creating greater stratum corneum hydration isn’t necessarily correct. Hydration of the stratum corneum is more dependent on natural moisturizing factors, intercellular lipids, and the structure of the composing corneocytes.

Like most studies of this nature, their conclusion is “maybe” and “requires further research”. The researchers thought it’s possible that increased water intake could be increasing “deep” skin hydration, but unfortunately, the experiment reporting those results didn’t explain how that was measured – so it’s not strong evidence. As well, different types of water were used; each region’s tap water will be different, as will each source of mineral water.

I do want to touch quickly on hyponatremia – also known as “water poisoning”. When too much water (especially deionized) is consumed very quickly – electrolyte levels can drop drastically which can lead to fluid moving into cells causing damage to the body. While everyone is different, the amounts needed to cause hyponatremia are quite large – one paper reported on soldiers who had died from hyponatremia found that the amount consumed was 10-20 litres in a few hours and was combined with exertive exercise.

My thoughts? Adding a litre or two of extra water a day isn’t going to transform your skin – but it probably isn’t a harmful habit either if the intake is spread out throughout the day.

Akdeniz M, Tomova-Simitchieva T,
Dobos G, Blume-Peytavi U, Kottner J. Does dietary fluid intake
affect skin hydration in healthy humans? A systematic
literature review. Skin Res Technol. 2018;00:1–7.
https://doi.org/10.1111/srt.12454

"Does drinking more water make your skin more hydrated?" on KindofStephen.

The most commonly used one is the Corneometer made by Courage-Khazaka. While there have been a few studies looking at differences in measurements between the Corneometer and other devices, like the Skicon made by I.B.S., very few have looked at how well they work at actually measuring the hydration of the skin. 

These devices measure either the conductance or capacitance of the skin. Conductance is the skin’s ability to conduct or pass an electrical charge, whereas capacitance is the measurement of the skin’s ability to hold a charge. The idea is that an increase in the capacitance or conductance of the skin indicates an increase in the amount of water within the skin. The Corneometer is based on skin capacitance, and the Skicon is based on skin conductivity.

The problem is that many things can increase the capacitance or conductance of the skin, like moisturizers. When you’re measuring your skin with one of these devices, you’re not just measuring the water in the skin…but also everything that’s dissolved in it.

An unpublished paper compared the Corneometer and Skicon against solutions of different substances commonly found in skin care products and found that they can have a large effect on the results. Increasing concentrations of salts like sodium chloride or calcium chloride increased the capacitance and conductance measurements of the devices. Different types of solvents like glycerin or ethanol also affected the readings, and the Corneometer tended to be more sensitive to dissolved substances than the Skicon.

So these devices should be left in the range of fun and interesting, but probably aren’t a great indication of actual hydration levels in your skin. Even if you apply it on the same area of skin, using the same type of water (tap water’s conductance and capacitance changes day to day), things like the room’s humidity, or if you’ve sweat recently will affect the readings. As well, using the devices on cleaned skin doesn’t capture the effect created by the moisturizer. 

Ideally one would measure the moisturizer, the skin with the moisturizer on, and then “cancel” out the effect from the moisturizer itself – but I think that is beyond what the consumer devices are capable of, especially the ones that rate skin hydration with smiley faces :)!

"Hi Stephen, I’ve seen those handheld skin analyzers popularized on several beauty blogs. But do they really work?" on KindofStephen.