Oxidants, Antioxidants, and Skin
Why antioxidants work - and why they work even better together.
The word “antioxidant” is very much in the vernacular, and most of us know antioxidants to be “good things” that help prevent and repair skin aging. Alchimie Forever, and many other skin care brands, was founded on the concept of antioxidant care.
But what, really, are antioxidants? Are some “better” than others? And how do they help our skin? The following post is an attempt to answer these questions, toeing the line between plain English and science-y nerdy English.
A couple of disclaimers before I dive in. First, I am neither a dermatologist nor a scientist. Second, this post was reviewed and approved by both a dermatologist (my father, Dr. Luigi L. Polla), and a scientist (my mother, Dr. Barbara S. Polla). Third, references to published papers are numbered, all details are available upon request in comments.
What Are Oxidants?
To understand antioxidants, we first need to understand oxidants – also known as Reactive Oxygen Species (ROS), of which free radicals (a term almost as vernacular as antioxidant) are a subset.
As the word indicates, oxidants are related to oxygen. We all know we can’t live without oxygen. As usual in science, however, nothing is black and white but rather shades of grey: while oxygen is essential to life, it is also the source of oxidants. Oxygen is metabolized in the body by successive reductions, leading to the creation of superoxide anion (O2.-), hydrogen peroxide (H2O2) and hydroxyl radical (.OH). These different molecules are all reactive oxygen species; some are free radicals (defined by the presence of an unpaired electron, not containing all of the oxygen species), whereas others are non radical (H2O2, singlet oxygen 1O2).
At low concentrations, ROS are an integral part of physiological processes and have precise intracellular functions: second messengers, gene regulators, mediators for cell activation and anti-infection weapons. Indeed, the first line of defense against micro-organisms starts with the production of large quantities of ROS by our white blood cells. Again, very little in science is black and white, but rather shades of grey…
What Are Antioxidants?
Antioxidants are molecules that neutralize ROS and / or limit the damage they can cause. The human body being what it is, human cells are equipped with a number of endogenous antioxidants such enzymes superoxide dismutase, catalase, glutathione peroxidase and thioredoxine reductase, and coenzyme-Q10 (1). In effect, we are all born with built-in antioxidant defenses in our bodies, available to help control the production of ROS. Unfortunately, the production of ROS typically outpaces the ability of these endogenous antioxidants to control them.
In many situations, ROS production exceeds the capacity of our endogenous antioxidant systems, which is why the supplementation of endogenous antioxidants with exogenous (not produced by the human body) ones is important, both topically (the subject of this post) and orally.
ROS, Oxidative Stress & Skin Aging
When the natural balance between oxidants and antioxidants is altered, either by an increase in the production of oxidants or by a decrease in endogenous antioxidants, bad things happen. Specifically, ROS potentially damage cellular structures, in what is called oxidative stress (2).
The exposure of the skin to UV is the main cause of oxidative stress (3): UV exposure induces the production of high quantities of ROS (in particular, singlet oxygen 1O2 and .OH). These ROS may damage DNA, lipids, membranes, intracellular and extracellular proteins and sugars. This is the scientific explanation behind why UV is bad for the skin, and why SPF protection, shade, and clothing are essential to preserve the skin’s health.
Over time, UV-induced DNA lesions (single-strand or double-strand breaks, DNA-protein crosslinks, and more) lead to the appearance of actinic keratoses and possibly carcinogenesis (4). UV-induced damage of lipids (lipid peroxidation) lead to the citrin (yellowish, leather-ish) appearance of the skin. UV-induced protein alterations (whether directly or indirectly via protease activation) lead to the progressive loss of collagen and elastin, characteristics of aged skin.
Many of the clinical aspects of accelerated skin aging related to the excessive exposure to UV can be explained by oxidative stress and prevented by an effective combination of sunscreen and antioxidants (5).
Types of Exogenous Antioxidants
The two types of exogenous antioxidants are synthetic (meaning lab-made) antioxidants and phytoantioxidants (meaning plant-based).
Two well-known synthetic antioxidants frequently used in skin care formulations are idebenone and tocopheryl acetate. Idebenone (INCI name: Hydroxydecyl Ubiquinone) is a short-chain synthetic analogue of the endogenous antioxidant coenzyme Q10. Tocopheryl acetate is a stable, esterified derivative of vitamin E (aka Tocopherol).
Phytoantioxidants, a large family of plant-based molecules, are also frequently used in skin care formulations. Let’s take a step back and think about why plants would be of interest in any conversation about UV protection. Plants are, like us humans, exposed to UV. They are, however, unlike us humans, unable to protect themselves by moving to the shade or applying SPF… As a result, they have had to develop very efficient strategies to defend themselves from ROS and protect themselves against the oxidizing stress induced by UV exposure. The goal of using phytoantioxidants in skin care formulations is to take these defense mechanisms plants have developed over thousands of years and apply them to the skin.
The majority of phytoantioxidants are polyphenols and carotenoids, which feature molecules such as flavonoids and anthocyanins. Three well-studied examples are green tea, grapes, and tomato.
Green tea contains catechins, epicatechin, epicatechin-gallate, epigallocatechin-3-gallate, all of them very efficient flavonoids. These antioxidant molecules scavenge ROS such as O2.-, .OH, H2O2 and 1O2. Studies show that epigallocatechin topically applied to a subject exposed to UVB inhibits the production of H2O2 in the dermis and the epidermis (6).
Grapes contain resveratrol and quercetin. Studies have shown that topical application of resveratrol was found to result in a significant inhibition of UVB effect on skin thickness and oedema (7). Resveratrol also inhibits UVB-mediated lipid peroxidation, due of the symptom of oxidative stress (7). Quercetin protects endogenous antioxidant systems and therefore enables their continued efficacy even after UV exposure (8).
Tomato is rich in lycopene, a carotenoid particularly known for its antioxidant and anti-carcinogenic properties when consumed orally and in great quantity (lots of tomatoes a day keep the doctors away). The powerful antioxidant properties of lycopene are probably related to its strongly reducing group: lycopene not only neutralizes the oxygenated free radicals but is also the most effective carotenoid in the scavenging of singlet oxygen 1O2. Lycopene can also scavenge free radicals, reduce lipid peroxidation, and prevent the erythema caused by UV exposure (9).
(Don’t worry, more about blueberries coming soon, when we discuss iron chelation.)
The Power of Synergies
Antioxidant math is as follows: 1 + 1 = 5.
Indeed, the natural combination of phytochemicals in fruits and vegetables is essential to their antioxidant activity. Studies suggest that the complex mixtures of phytochemicals present in whole foods explain the benefit of a diet rich in fruits and vegetables (10). It is probably also why no single antioxidant can replace the combination of the natural phytochemicals as provided in fruits and plants (i.e. whole tomatoes are more powerful than lycopene extract). Furthermore, phytoantioxidants differ in terms of molecular mass, polarity and solubility. These differences affect their biological availability and their specific distribution and effects (10). Studies also show that the combination of three antioxidants is more effective to prevent oxidative stress than a single molecule, even if it is a strong antioxidant (11).
So Now You Really Know
You already knew antioxidants were good for skin health. Now, you know (more about) why, and how. Very practically, here is what you can do to lead an antioxidant lifestyle: Eat antioxidant-rich foods. Favor a diversity of antioxidants. Choose whole fruits and vegetables over isolated molecules. Use antioxidant-rich skin care. And of course, stay out of the sun and always wear SPF.