SKINIPEDIA - Skin Encyclopedia: Protecting Skin
Protecting Skin with Antioxidants
WHILE IT HAS been almost 50 years since the free-radical
theory of aging was first proposed, it is still one of the
most widely accepted theories to explain the cause of aging. Fortunately, our bodies have a natural defense mechanism to help us from succumbing to this constant free-radical assault. The bad news is, as with everything else in life, it seems to be less effective with time. And although our bodies may be naturally equipped to fight off these free radicals, they can still lead to inflammation and premature aging, which often manifests itself adversely in the skin. One of the means we have to fight free radicals is the use of antioxidants, which also protect our skin. In order to understand how these antioxidants work, we need to look more closely at how free radicals form.
Free radicals … what are they?
Free radicals may be formed through natural human physiological
processes as well as from the environment. They may be the result
of diet, stress, smoking, alcohol, exercise, inflammation, drugs or
exposure to sunlight and air pollutants. While there are many types
of free radicals that can be formed, the most common in aerobic
(oxygen breathing) organisms are oxygen free radicals, often
referred to as reactive oxygen species, which includes superoxides,
hydroxyl anions, hydrogen peroxide and singlet oxygen. Let’s look
at an oxygen molecule to see how a free radical forms.
An oxygen molecule is made up of two
atoms of oxygen. Each atom contains a nucleus,
neutrons, positively charged protons and
negatively charged electrons. The protons in
the nucleus are balanced by the same number
of electrons that surround the nucleus. In the
case of oxygen, there are eight electrons and
eight protons. It is the electrons revolving
around the nucleus that are involved in chemical
reactions; they are also responsible for
bonding atoms together to form larger molecules.
The electrons surround the nucleus of
the atom and “orbit” the atom in one or more
shells. The innermost shell is full when it has
two electrons. This comes as no surprise as
electrons generally hang out in pairs. When
the first shell is full, the remaining electrons
start to fill in the outer shells. While the first
shell only holds two electrons, the second shell
holds eight electrons. Because we already have
two electrons in the inner shell we only have
six electrons left to accommodate.
It is important to understand that an
atom’s chemical behavior is determined by
the number of electrons in its outermost
shell. When the outermost shell is full, the
atom is stable and tends not to engage in
chemical reactions. When, however, the outermost
shell is not full, the atom is unstable.
It will try and stabilize itself by either gaining
or losing an electron to either fill or empty its
outermost shell. Or it will share its electrons
by bonding with another atom that is also
looking to complete its outer shell. It is not uncommon for an atom to complete its outer
shell by sharing an electron with another
atom and forming a bond.
Let’s go back to the oxygen atom. We said
it had eight electrons orbiting its nucleus.
Remember, the inner shell can accommodate
two electrons and it is full; that leaves six
electrons orbiting around the nucleus in the
outermost shell. In order to be stable it would
need eight. So what does the oxygen atom do?
It buddies up with another oxygen atom and
shares electrons in its outer shell. Because they
both are short two electrons, they form a weak
double-bond, sharing four of the electrons. In
essence each atom now feels like it has a full
outer shell, all electrons are paired and the
molecule is stable. Free radicals form when
one of these weak bonds between electrons is
broken and an uneven number of electrons
are left with an atom. This means the electron
is unpaired, making it chemically reactive. It
will now try and steal an electron from a
neighboring molecule to stabilize itself.
Unfortunately, oxygen is very susceptible to free-radical formation and with aerobic organisms this can be lethal. Oxygen free radicals are implicated in the overall aging process and are responsible for photoaging, cancer and inflammation in the skin. Studies have shown that reactive oxygen intermediates causes, in part, UV-induced damage to the skin. Oxygen free radicals cause lipid per- oxidation, which results in damage to cell membranes and this can cause premature aging, skin cancer and cell death.