If you yearn for smooth skin that
glows with youth, the chances are
that at some point you will have heard
the exhortation to drink lots of water
in order to flush out those evil toxins
and keep your skin healthy.
The exact amount people suggest
varies. US-based advice tends to
recommend eight glasses a day, while
in hotter climates people are advised
to drink more to compensate for
higher rates of sweating. But
regardless of the exact volume of
water suggested, the principle behind
the advice remains the same – taking
extra water on board will keep your
skin hydrated. In other words, water
acts like a moisturiser, but from the
inside out.
This is such a common idea you might
be surprised at the lack of evidence to
back this up. You might expect there
to be countless studies where people
are separated into two groups, one
assigned to sip water all day, the
other to drink a normal amount. Then
the smoothness of the skin could be
assessed a month or so later to
establish whether sipping more led to
smoother skin.
In fact such studies are rare, partly
because water can’t be patented, so
it is hard to find anyone to fund such
research when there will be no new
medication or cosmetic to sell that
could repay the costs. A review by the
dermatologist Ronni Wolf at the
Kaplan Medical Centre in Israel found
just one study looking at the effect
of long-term water intake on the
skin. But the results were
contradictory. After four weeks, the
group who drank extra mineral water
showed a decrease in skin density,
which some believe suggests the skin
is retaining more moisture, while
those who drank tap water showed an
increase in skin density. But
regardless of the type of water they
drank, it made no difference to their
wrinkles or to the smoothness of their
skin.
That’s not to say that dehydration
has no effect on skin. We can
measure some effect through the
assessment of skin turgor. This is a
measure of how fast it takes the skin
to return to normal if you pinch some
skin and lift it up. If you are
dehydrated your skin will take longer
to get its shape back.
But it doesn’t follow that because
drinking too little water is bad for the
skin, drinking above average
quantities is good. It would be like
saying that because a lack of food
leads to malnutrition, overeating
must be good for us. Or as Wolf puts
it, it’s like saying a car needs petrol,
therefore the more petrol the better.
Mystery advice
Another common belief is that if you
drink extra water the body will
somehow store it. But it depends on
how fast you drink it. Drink several
glasses within a fifteen-minute
period and you will just pass extra
urine. If you spend more than two
hours sipping the same amount, more
liquid is retained.
There is one study suggesting that
drinking 500ml of water increases the
blood flow through the capillaries in
the skin. But the skin was only
evaluated thirty minutes after
drinking the water, and what we don’t
know is whether this in turn improves
skin tone.
One counterargument is that skin
contains up to 30% water, and this
helps it to look plump. This may be
true, but the skin’s youthful
appearance is affected more by
factors such as genetics, exposure to
the sun and damage from smoking.
So the mystery is where the eight-
glasses-a-day recommendation for
good skin comes from. Few of the
official guidelines even refer to the
skin. Water is undoubtedly the most
important nutrient for the body.
Without it we die in a matter of days,
and there are of course other health
benefits from staying hydrated. A
review in 2010 found good evidence
that it reduces the recurrence of
kidney stones in those who have
already had them, but evidence for
other specific benefits is weaker.

water is great for the skin and body!