“Drink more water to hydrate your skin”. You’ve probably heard it, and it’s easy to see why this is common advice – it’s cheap, sounds right, and feels healthy…but is it true?

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