Moisturisers
How do moisturisers work?
What makes our skin
the way it is?
veryday we wash, buff
and apply creams to our
skin, but how much do
we really know about the
complex structure covering
our bodies?
E
Jonathan
Crowther
Research Scientist at
Procter & Gamble,
explains the science
behind moisturisers...
In simple terms, our skin is made
up of three distinct layers: the
top or outer layer called the
epidermis; the second layer
called the dermis, which
contains blood vessels, nerve
endings, hair roots and sweat
glands; and finally the
subcutaneous fat layer
containing larger blood vessels
and nerves.
We all appreciate that when our
skin is dry it often feels rough
and flaky. It's the top layer of
the epidermis – the stratum
corneum – that plays a key role
in helping contain moisture
within the skin. Normally up to
15% of the stratum corneum
consists of water. When the
moisture content of the stratum
corneum falls below 10% the
skin appears dry and flaky;
further drying can lead to
reduced flexibility and cracking.
The spaces between the cells in
the epidermis are packed with
fats, or lipids, and other
components. A mixture of
amino acids and salts, which are
water soluble and present within
the cells and help the cells hold
in their moisture, is known as
the ‘natural moisturising factor’.
This is important as it helps the
stratum corneum regulate
natural water loss by preventing
water evaporating from deeper
layers of the skin. The mixture
of amino acids and salts are
easily washed out (being water
soluble), which reduces the
ability of the cells at the surface
to hold on to their moisture.
Sometimes when we use strong
soaps or detergents, or are
exposed to solvents, these
valuable components are
washed out and the skin loses
some of its ability to keep
water; it then becomes dry and
will start to crack.
Skin cells are constantly being
renewed and the dead cells
shed. The epidermis contains
natural enzymes that are
important for getting rid of old
skin cells. These enzymes need
moisture to work properly.
What does moisturiser
consist of and how does
it work?
Moisturiser can play a key role
in both adding water to the skin
and keeping it hydrated.
In terms of facial moisturisers,
most are made up of oil-inwater emulsions consisting of
tiny droplets of oil held in a
watery base. To prevent the oil
and water from separating or
deteriorating, manufacturers add
stabilising ingredients, such as
emulsifiers and thickeners.
In order to help keep water
in the skin, moisturisers contain
substances called humectants.
These are substances that are
capable of attracting water
and help to conserve the water
in the skin. One of the oldest
and best examples is glycerin,
sometimes called glycerol. This
has been the standard humectant
for many decades based on its
excellent safety record.
Moisturisers
In the case of dry skin, the skin
cells are being shed too fast.
Rather than being shed
individually these come off in
clumps that look like white
flakes. Repeated application of
moisturiser increases the water
content and normalises cell
turnover. This is why it is
important to continue using a
moisturiser on the skin.
Because most cosmetic
moisturising products have
a water base they need
preservatives, to stop them
being contaminated by
micro-organisms. These are
everywhere in the environment
as well as on and in our bodies.
Without preservatives, microorganisms would rapidly spoil
the product, and even cause it
to become a risk to health.
So, what does a moisturiser
basically consist of? A cosmetic
moisturiser designed to
encourage skin hydration will
be made from water and
humectants, blended with oils
and emulsified to form a
liquid or cream.
How can moisturisers
make our skin look
visibly better?
Adding moisturiser means that a
liquid now fills the air gap
between the dry skin flakes and
the skin rather than just air, this
liquid has a closer refractive
index to that of skin and as such
helps to transmit light rather
than reflect it. With increasing
moisture levels, the stratum
corneum becomes more
translucent and this means more
light can reach the lower layers
of the skin. This is responsible
for the apparent enhancement
of skin colour that is often
visible the moment you apply
a moisturiser.
New innovations
Recently moisturisers have been
developed which offer sunless
tanning. One of the most
effective ingredients for sunless
tanning is dihydroxyacetone
(DHA). The tan itself is not a
dye, stain or paint, but is
formed during a chemical
reaction between the DHA and
amino acids in the uppermost
layer of the skin surface – the
stratum corneum. This reaction
is similar to one well known to
food chemists called the
Maillard reaction (the browning
process which occurs during
food manufacturing and
storage). It does not involve
skin pigmentation nor does it
need UV exposure to initiate
the color change. The reaction
is non-toxic and skin safe,
without the damage associated
with UV exposure. The tan is
temporary and fades slowly
over three to ten days.
How many times have you
read that skin absorbs 60% of
whatever is applied to it? Yet
there is no evidence to support
this figure. In practice, the skin
will absorb anything from 0%
to 100% of whatever contacts
it but in general the primary
function of the skin is to act
as a barrier that prevents the
intrusion of external materials.
Cosmetic companies actually
have to work hard to develop
formulations that can be
absorbed into the skin to
deliver all the benefits the
consumer expects.
The CTPA is the trade association for the UK cosmetic, toiletry and perfumery industry.
For further information on cosmetic products and their regulation, visit www.ctpa.org.uk