It is commonly accepted that environmental exposure causes approximately 50% of extrinsic premature skin aging. Known as the free radical theory of aging, environmental exposure creates free radicals which are believed to be a major contributor of accelerated skin aging. Consumer awareness of free radicals is growing rapidly with 14% of global consumers believing them to be a major cause of their skin and hair problems.
We now know that all parts of the solar spectrum can cause free radical formation. Solar radiation is believed to contribute up to 80% of extrinsic skin aging, with visible light contributing around 52% of free radicals, UVA/B 6%, and infrared radiation (IR) A/B/C 42% (1).
Over a lifetime, free radicals can cause accumulated damage, leading to a decline in skin structure and function (2). Daily environmental exposure creates free radicals resulting in chronic low level skin inflammation/irritation. This is probably due to the activation of Nuclear Factor Kappa B (NF-KB) which can cause the release of inflammatory cytokines such as Interleukin 6 and 1 Alpha. Over time, this can lead to skin wrinkling, sagging, increased DNA damage, and a reduced ability to repair DNA damage (3).
What are free radicals?
Free radicals, referred to as Reactive Oxygen Species (ROS), are molecules derived from molecular Oxygen. Oxygen has two unpaired electrons in separate orbitals in its outer electron shell. This structure makes Oxygen susceptible to forming Singlet Oxygen radicals, Superoxide radicals, Hydroperoxide radicals, Peroxy Nitrite, Alkoxyl radicals, Hydroxyl radicals, and Nitrogen Monoxide.
Singlet oxygen is probably the most reactive, destructive form created when a photo excited molecule absorbs and transfers energy to Oxygen. It is the most reactive type of ROS and is responsible for much of the skin damage caused by environmental aging.
Human skin contains numerous endogenous molecules that can create singlet Oxygen when they absorb radiation and go into an excited state. Solar radiation can cause electrons to jump to a higher energy orbital called the singlet state.
Once excited, the molecule may quickly return to the ground state by emitting a photon or it can decay to a less energetic excited state called a triplet state before finally getting rid of its energy as heat and returning to the ground state. While in the singlet or triple states, molecules are very reactive and can transform to a less reactive form or react with molecules in skin. Free radical quenchers rapidly deactivate photo excited molecules to the ground state. Typical antioxidants can’t do this.
Ground state Oxygen can directly absorb 765 nanometers (nm) visible light leading to the formation of singlet Oxygen without the involvement of a photosensitizer or excited molecule. Infrared B can also cause the direct conversion of ground state Oxygen to singlet Oxygen (4).
Most antioxidants, except for Carotenoids, have very weak activity against singlet Oxygen. That is why the highest concentrations of Carotenoids in the body occur in skin where they are the primary antioxidants that protect against environmentally induced free radicals (5).
Current sunscreens offer only partial protection against free radicals formed by UV and little against those formed by Ozone, visible light, blue light, and Infrared. Even photo stabilized sunscreens can still generate free radicals.
How do antioxidants in skincare work?
Many antioxidants added to formulations are weak at preventing ROS formation and most work by neutralizing free radicals once formed where they are consumed during the process. Antioxidants function by slowing or preventing the oxidation of other molecules by donating an electron to prevent free radical formation or neutralize existing ones. They can slow down and can even prevent some of the oxidative damage that causes skin aging. Since antioxidants block the process of oxidation by neutralizing free radicals, the antioxidants themselves become consumed. That is why there is a constant need to replenish the antioxidant supply.
Antioxidants work by several different mechanisms:
- Chain-breaking- When a free radical steals an electron, a second radical is formed. This molecule in turns does the same thing to a third molecule continuing to generate more instability. This process continues until either the free radical is stabilized by a chain-breaking antioxidant such as beta-carotene, vitamins C and E, or it decays into a harmless product.
- Prevention- Antioxidant enzymes can prevent oxidation by reducing the rate of the chain initiation. By neutralizing the initiating radicals, antioxidants sometimes prevent an oxidation chain from starting.
What are free radical quenchers?
Free radical quenchers are a second-generation antioxidant technology that work by rapidly returning photo excited molecules to the ground state before they can react with other molecules. Conventional antioxidants offer only weak protection against singlet Oxygen, the most damaging type of free radical. Quenchers are different from conventional antioxidants in that they can rapidly deactivate photoexcited molecules, helping to neutralize any singlet Oxygen formed.
They also can help stabilize photo sensitive molecules like Retinol, Avobenzone, Tocopherol, perfumes, skin lipids, and Carotenoids often more effectively than conventional antioxidants.
Commercially available quenchers
- Ronacare AP (Bis-Ethylhexyl Hydroxydimethoxy Benzylmalonate-EMD) protects against UV induced free radicals, protects endogenous skin lipids and antioxidants from oxidizing.
- Synoxyl HSS (Trimethoxybenzylidene Pentanedione -Sytheon) is positioned as a triple state quencher for photo stabilizing Avobenzone, and has also been shown to boost in vivo SPF by up to 50% for both organic and inorganic sunscreens.
- Solstay S1 (Ethyl Hexyl Methoxycrylene-Hallstar) is positioned as a triple state quencher to photo stabilize Avobenzone, Resveratrol and Retinol. It can also stabilize antioxidants.
- Micah (Bis (Cyano Butylacetate) Anthracenediylidene-Hallstar) is shown to inhibit visible light induced free radicals, UVA induced inflammatory cytokines like Interleukin 6/1-Alpha and matrix metallo proteases.
- Synoxyl AZ (Acetyl Zingerone-Sytheon) has been clinically shown to reduce wrinkles, skin hyperpigmentation, and reduce UV induced skin redness. It may also have better efficacy due to its chelating activity.
- AgeCap Smooth Cosmetic Ingredient (Methoxyhydroxyphenyl Isopropylnitrone-Dow Chemical) has been clinically shown to reduce wrinkles and improve skin radiance. It performed well when tested versus Vitamin C and Retinol in an 84 day clinical.
Note: Not all Quenchers behave the same way. Quenchers like Synoxyl HSS and Solastay S-1 can photo stabilize Avobenzone but may not be able to neutralize free radicals formed by excited chromophores in the skin.
I believe that free radical quenchers combined with conventional antioxidants should be added along with sunscreens to all day wear SPF products as an added line of defense. Some quenchers also may be more effective than antioxidants in stabilizing fragrances and highly unsaturated ingredients on skin.
References
- Effect of the sun on visible clinical signs of aging in Caucasian skin: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790843/
- UV, visible and infrared light. Which wavelengths produce oxidative stress in human skin?: https://www.ncbi.nlm.nih.gov/pubmed/19319493
- NF-κB signaling pathway and free radical impact: https://www.ncbi.nlm.nih.gov/pubmed/22855720
- Endogenous Generation of Singlet Oxygen and Ozone in Human and Animal Tissues: Mechanisms, Biological Significance, and Influence of Dietary Components: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4799824/
- The Role of Carotenoids in Human Skin: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6264659/
The views, opinions and technical analyses presented here are those of the author or advertiser, and are not necessarily those of ULProspector.com or UL Solutions. The appearance of this content in the UL Prospector Knowledge Center does not constitute an endorsement by UL Solutions or its affiliates.
All content is subject to copyright and may not be reproduced without prior authorization from UL Solutions or the content author.
The content has been made available for informational and educational purposes only. While the editors of this site may verify the accuracy of its content from time to time, we assume no responsibility for errors made by the author, editorial staff or any other contributor.
UL Solutions does not make any representations or warranties with respect to the accuracy, applicability, fitness or completeness of the content. UL Solutions does not warrant the performance, effectiveness or applicability of sites listed or linked to in any content.
I’m trying to learn more about pro-oxidation within formulations. There seems to be little to no available info on the web however from what I can remember it seemed to be a pretty big deal. Can you point me in the right direction?
Hi, Tyrick:
See UL Prospector article about antioxidants.
https://www.ulprospector.com/knowledge/2963/pcc-antioxidants-powerful-skin-care-actives-stabilizers/
Thanks for reading,
George