• Núria Estapé, science journalist

    The water myth: How much should we drink?

    10 Jun

    It is widely believed that we should drink at least two litres of water a day to keep our skin hydrated. This myth is rooted in the fact that people – doctors included – are concerned about the health of the skin. Scientific evidence has, however, undermined this belief.  Drinking plenty of water is healthy, but it does not ensure a smoother skin.


    Drinking two litres of water a day to properly hydrate the skin is a belief that emerged strongly in the 20th century and that caught on through beauty magazines and especially the Internet. One version promises that following the so-called 8x8 rule daily (drinking eight glasses of eight ounces each, or almost two litres, of water) makes the skin more elastic, prevents it from drying out and makes it less likely to wrinkle.

    The boom in personal aesthetics and the cult of the body probably caused this idea to spread, to the point where no one dared question it. But evidence-based medicine and new knowledge regarding the metabolism of fluids have helped undermine this long-standing myth.


    Water: used or eliminated

    The skin contains about 30% of the water in our body. Water is in the blood, flowing through the vessels that irrigate the skin, and is also in the fluid in the interstitial space between cells. Water also forms part of the skin cells and is essential for their metabolism.  The stratum corneum (the outer skin layer), composed of horny cells separated by lipids (fats), serves as a barrier that limits the amount of water entering or leaving through the skin.

    The organs of the human body, including the skin, are designed not to store large amounts of water but to prevent water from being wasted when it is needed.  The skin uses water when it needs it and otherwise eliminates it. Thirst is the best indicator: if the level of water in and around the cells of our body falls, we feel thirsty. This circuit is designed to maintain a balance – which means that there is no need to force oneself to drink if not thirsty.


    From myth to reality

    Our body needs about two and a half litres of liquid each day.  We normally drink about 1.7 litres of water and other liquids, and the remainder we extract from the food we eat. The 8x8 rule requires us to drink almost a litre more of water, which facilitates the work of the kidneys and has no negative effects on the body.

    But there is no scientific evidence indicating that drinking more water changes the fluid content of the skin, unless this is accidentally dehydrated. One particular study that examined the skin characteristics (density, thickness and morphology) of healthy volunteers who had drunk a lot of water reported that the 8x8 rule does not guarantee a smoother wrinkle-free skin. The morphology, and hence the appearance, of the skin, is not affected by consuming too much or too little water.


    Psycogenic polydipsia

    American dermatologist Katie Rodan, co-author of the book Write Your Skin a Prescription for Change, joked about the 8x8 myth, saying that our skin is not like a plant because, if it were, it would perk up visibly after a glass of water. The water we drink does not go directly to the skin: it first passes through the intestines and is absorbed by the blood before eventually reaching the skin cells. There are several mechanisms that regulate its metabolism, which always tends toward equilibrium.  Drinking a lot of water without being thirsty is not beneficial for the skin or for any other organ.

    In fact, drinking a lot of water very quickly (between 700 ml and one litre per hour) can even be dangerous, as this quantity is beyond the elimination capacity of the kidneys. Psycogenic polydispia, which refers to the compulsion to drink (seven litres of water a day or more), can alter the body’s water balance, lead to a loss of minerals such as sodium, potassium or magnesium, and cause cramps, fatigue, mental confusion and even coma.


    The skin is not affected

    It is clear that drinking plenty of water is beneficial for many body functions.  Water intake should certainly be increased in hot weather, when doing sport or in the event of a fever.

    But when it comes to the texture of the skin, drinking a little or a lot of water has a minimal impact, as demonstrated by a famous article by Dr Ronni Wolf and co-workers, of the Kaplan Medical Center (Rechovot, Israel). The appearance of the skin only improves, in fact, in response to the application of moisturizers that prevent moisture loss by evaporation. The belief that drinking lots of water improves the skin is nothing more than a myth.



    American Journal of Physiology

    Skin, Hydration and Health