Development of a new generation of sunscreens that provide protection through the full ultraviolet radiation spectrum has become a major focus. Furthermore, studies and findings presently validating the intrinsic component in preventing photoaging are long overdue.
Photoaging, a term given to chronically sun-exposed skin, is characterized by deep wrinkles, pigmentation, lentigenes, leathery skin, and conditions such as poikiloderma, which displays vascular and pigmentary changes. Photoaged skin shows a lessening of cutaneous microvasculature, leading to decreased skin temperature and nutritional supply. This reduces the cell’s ability to function and consequently, the skin’s reparative processes.
Ultraviolet rays activate matrix metalloproteinase (MMP) enzymes which disrupt the lipid barrier, breakdown collagen and elastin, and contribute to dry, dull, photodamaged skin. UVA and UVB exposure depletes cellular antioxidants and results in the production of reactive oxygen species (ROS). Averting photoaging includes prevention of ultraviolet penetration into skin as well as the inhibition of inflammation by antioxidants, which can be achieved through both intrinsic and extrinsic methods. Various skin rejuvenation therapies, ranging from topical home care to clinical treatments such as peels, IPL, or laser treatments, may offer some reversal of photodamage.
Controversy continues to persist regarding the amount of ultraviolet exposure needed to achieve healthy vitamin D levels and the photo conversion of 7-dehydrocholesterol to vitamin D3 (cholcalciferol). To add to the confusion, some studies indicate that a certain amount of sun exposure may actually protect from sun damage by converting vitamin D3 generated under the skin by sunlight and inducing T cells to migrate to the skin, thereby boosting the skin’s immunity. However, 10 to 15 minutes of sun exposure (without sunscreen) three times per week is enough to produce the body’s requirement of vitamin D. Furthermore, many experts agree that people who are repeatedly exposed to high levels of ultraviolet light are actually suppressing their immune system. Ultraviolet damage creates a state of oxidative stress in the body, adding to its susceptibility to degenerative disorders, macular degeneration, and, of course, skin cancer.
Understanding the Ultraviolet Rays
In order to choose the defense arsenal for clients, it is important to know the different types of ultraviolet rays and their effects on skin. Ultraviolet radiation is part of the light spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. Visible light falls between 400 to 700 nanometers. A nanometer is billionths of a meter.
UVB radiation (shortwave rays) is still considered to be the major factor to blame for the harmful effects of sun exposure. It is responsible for sunburn and incites damage in the superficial epidermis. UVB is absorbed by the stratum corneum and is partially blocked by the ozone layer. Its rays penetrate 290 to 340 nanometers. Depending on the time of day, season, and location, UVB rays vary in intensity. They bounce off of reflective surfaces such as water, ice, and snow, therefore doubling the hit, which is why most people get their worst sunburns when in these elements. Ultraviolet rays do not penetrate glass significantly.
UVA penetrates the skin more deeply, as it is the longest of the three wavelengths at 320 to 400 nanometers. It is further divided into two wave ranges, UVA-1 at 340 to 400 nanometers and UVA-11 which measures 320 to 340 nanometers. The detrimental effects of UVA rays (long wave rays) are increasingly documented. They instigate DNA damage in the keratinocytes where cancer cells originate. Aged skin undergoes advancing disorientation of dermal collagen and elastic fiber bundles in photoaged skin; there is a considerable increase in disorganization and space between fiber bundles and thinning of fibers. UVA radiation produces significantly more of this breakdown, causing deep lines and sagging. It accounts for 95 percent of ultraviolet radiation and although they are less intense than UVB rays, UVA rays are 30 times more prevalent. They can penetrate glass and clouds and have relatively equal intensity throughout all hours of daylight. UVA is known as the tanning ray. A tan is an injury and represents the skin’s imperfect attempt to prevent DNA damage.
UVC rays are very short in comparison to the others; therefore, they are not a concern, as most UVC rays are absorbed by the ozone and do not reach the earth. UVC radiation emitted from artificial light sources can cause DNA damage in cells to the level of spinous layers, but it does not penetrate to the basal layer. One concern that has advanced over the last few decades is the decreasing thickness of the ozone. The potential impact to the skin can be explained by this general rule: a 10 percent reduction in the ozone layer causes about a 20 percent increase in UVB radiation and a probable 40 percent increase in skin cancers.
Labeling guidelines for sunscreens continue to evolve in the United States, albeit very slowly. The FDA issued a broad new set of statutes in June 2011, which took effect in 2012. These include:
- To be classified as "broad spectrum," sunscreen products must provide protection against both UVA and UVB radiation, with specific tests required for both.
- The maximum SPF value allowed on sunscreen labels is "50."
- "Sunblock," "instant protection," and "protection for more than two hours" are all prohibited without distinctive FDA approval.
- Statements of products being "waterproof" or "sweat proof" are prohibited.
- "Water resistance" claims on the front label must indicate how long the sunscreen remains effective and denote whether this applies to swimming or sweating, based on standard testing.
- Sunscreens must include standardized "drug facts" information on the container. However, there is no regulation that mandates mentioning whether the contents contain nanoparticles of mineral ingredients.
- Powder sunscreens are no longer allowed under current FDA regulations.
- The FDA is investigating the safety of spray-on sunscreens that can be harmful when inhaled, but are still allowed to be sold.
Swiss chemist Franz Greiter launched the "sun protection factor" (SPF) in 1974, which has become a worldwide standard for measuring the effectiveness of sunscreen. The FDA adopted the SPF calculation in 1978.
SPF is a measurement of sunburn protection, caused by UVB rays. The SPF is an imperfect measure of skin damage because the numbers do not reflect the degree of protection from UVA rays. UVA radiation does not principally induce reddening or pain, yet is responsible for invisible damage, triggering skin aging and cancer. SPF ratings can be confusing or misleading. High-SPF products can create a false sense of security because they offer trivial additional sun protection, yet contain higher concentrations of allergenic or irritating ingredients.
What are the Choices?
Currently, there are 17 active sunscreen ingredients approved by the FDA. In comparison, Europe has 29, Australia 26, and Canada 21.
Sunscreen ingredients are divided into two categories: Organic chemical ingredients that absorb ultraviolet light, and inorganic metal oxides (particulates) – such as titanium and/or zinc oxide, also known as physical screens – that reflect or scatter ultraviolet light.
A promising sunscreen ingredient, Tinosorb M, is an organic particulate that provides a duo-effect by absorbing light as do organic chemical ingredients, but also contains multiple chromophores that reflect or scatter a fraction of light like inorganic particulates. Tinosorb M is not yet FDA-approved but is available in Europe, Australia, and other countries. It is micronized to fine particles, is photo stable, and provides approximately 90 percent absorption and 10 percent reflection.
Avobenzone (Parsol 1789) may offer the best UVA radiation protection of currently FDA-approved chemical filters with little evidence of skin penetration. Avobenzone alone breaks down when exposed to sunlight and must be stabilized with other chemicals such as octocrylene.
The chemicals Mexoryl SX (Ecampsule) and Mexoryl XL developed by the French company LaRoche Posay (an L’Oreal brand), are UVA radiation filters. Mexoryl SX is water soluble. It absorbs ultraviolet rays, then releases them as thermal energy. It does not protect against the entire ultraviolet spectrum, so is combined with other ultraviolet filters. There is no demonstrated skin penetration. It is FDA-approved and patent held by L’Oreal. Mexoryl XL is oil soluble and has similar properties to Mexoryl SX, but is not FDA-approved. However, both are used synergistically in Europe.
There are a few other ingredients approved in the United States that are no longer or rarely used in sunscreens, including menthyl anthranilate, trolamine salicylate benzophenone-4, benzophenone-8, aminobenzoic acid (PABA), and padimate O (a PABA derivative). PABA is banned for sale in Europe, and both PABA and padimate O absorb UVB rays, creating cellular damage and producing indirect DNA damage.
Prior to the approval of avobenzone and mexoryl SX as UVA radiation filters, oxybenzone offered the only satisfactory UVA protection outside the inorganic particulates (zinc oxide and titanium dioxide). Numerous studies have demonstrated the potential health risks of oxybenzone. In a 2008 study, The Centers for Disease Control and Prevention detected oxybenzone in 97 percent of 2,500 Americans tested, both children and adults. A second study found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls. This ingredient has been shown to disrupt normal hormone functions and have photocarcinogenic effects. While controversial, oxybenzone continues to be a popular sunscreen ingredient, providing absorption of both UVB and shortwave UVA rays.
Benzophenones are controversial and their use in sunscreen products now warrants a warning label in the European Union. Most ultraviolet filters are esters which, if absorbed through the skin, are converted to metabolites and excreted by the body. Benzophenones are aromatic ketones which tend to be more resistant to routine metabolism and excretion in the body, making their accumulation in fatty tissue more likely.
Neither titanium dioxide nor zinc oxide can be used in their raw form; therefore, they are synthesized in order to make them appropriate for use in cosmetic formulations. Zinc oxide does occur in nature as the mineral zincite, but it is quite rare and commercially unavailable. Zinc oxide is unique among sunscreen ingredients in that it is truly a broad-spectrum reflector, protecting from UVA, UVB, and even UVC radiation. Titanium dioxide is effective at blocking UVB rays and shortwave UVA rays, but it is not as effective as zinc oxide at blocking longwave UVA rays. Unlike organic sun-blocking agents, these metal oxides do not degrade with exposure to sunlight.
Most sunscreens use zinc oxide particles that have been coated with an inert substance. Some companies use a zinc oxide powder that they state is a natural, “nature identical mineral,” and this term applies to uncoated zinc oxide, which has been mined. Uncoated zinc oxide is somewhat more photo reactive, does not mix well with other ingredients, and gives the heavy, white coating associated with zinc. It is used in calamine lotion and diaper rash cream. Many people may prefer natural ingredients, but most zinc oxide and titanium dioxide used in skin care formulations, although very safe, is not 100 percent natural. The chemical treatment of the ores, followed by micronization or nanonization to a suitable particle size and then coating with aluminum derivatives or silica to reduce the reactivity, makes these products synthetic in character and invalidate the natural claim. Titanium dioxide is regarded as safe in a non-nanonized form, which is different from micronized due to particle size. A micronized particle is significantly larger than a nanonized particle. Nanonizing particles makes them absorbable through the skin, as well as inhalable, posing a potential health risk. Micronizing, or nanonizing, titanium dioxide or zinc oxide, give them more “slip” and eliminates the white coating associated with these ingredients.
Zinc oxide and titanium dioxide are allowed in products up to 25 percent, compared to only three percent for avobenzone, cinoxate, and dioxybenzone.
Natural and Plant-Based Protection
To date, there are no FDA-approved natural ultraviolet filters. However, botanical-based, photo-protective actives strengthen the skin’s immune response to photodamage, complement classical sunscreens, and reserve residual damage.
Dunaliella sanila is micro algae that is rich in antioxidants carotenoids, phytoene, and phytofluene. In vitro studies revealed that phytoene absorbs light in the UVB range, and phytofluene in the UVA range. These carotenoids protect against oxidative damage and inflammation and inhibit melanin synthesis. Resveratrol is an antimicrobial substance produced by plants in defense against stress, infection, and ultraviolet radiation. Resveratrol is a potent antioxidant that scavenges free radicals and prevents lipid peroxidation. Studies have shown that topical resveratrol inhibits UVB-induced oxidative stress and prevents UVA radiation damage and abnormal cellular proliferation.
Gamma oryzanol, a rice bran derivative, is approved in Europe as an UVA/UVB filter, due to its high resistance to ultraviolet light and antioxidant properties. Bran extracts inositol and inositol hexaphosphate protect human skin cells from UVB radiation and have been shown to have anti-tumor capabilities.
A John Hopkins University study shows that skin treated with broccoli sprout extract, sulporaphane, exhibits significantly reduces ultraviolet radiation erythema. What is interesting about this extract is that it works inside skin cells, boosting enzymes that protect against ultraviolet radiation; the effects last several days after the extract has been removed. Topical caffeine decreases the skin’s roughness and wrinkles after UVB exposure, and pomegranates strengthen the epidermis, increasing its resistance to UVB rays due to their powerful catechins and anthocyanins. Vitamin A (retinol, retinyl palmitate) greatly reduces the effects of sun-induced skin damage, including actinic keratosis, fine lines and wrinkles,
Supplements offer an added layer of protection, since people rarely use sunscreens as directed, and miss areas of the skin or forget to reapply it. Internal support, through supplements, provides not only photo-protective benefits for the skin, but enhances overall health due to their potent antioxidant activity. Being systemic, supplements offer the advantage of protecting the entire skin surface and not being washed away by bathing or perspiration. However, they certainly do not offer sufficient protection to replace topical sunscreens.
Natural fern extract (polypodium leucotomos) has shown significant photo-protective effects in both in vitro and in vivo studies. CoQ10 suppresses ultraviolet-induced MMP1 production of fibroblasts. Astaxanthin inhibits ultraviolet radiation-induced metalloproteinase 1 production. An anti-inflammatory diet, emphasizing a paleo approach, offers the most benefit for the skin (and body!) when it comes to sun exposure. These foods include healthy saturated fats, green leafy vegetables, omega-3 rich foods like fish, and antioxidant-containing foods like watermelon, berries, green tea, dark chocolate, and coffee (the last two being my favorite).
The unchangeable natural aging process is dependent on time and genetics. However, photoaging can be evaded with good sun protection practices and healthy lifestyle choices.
Krista McKowen, a licensed aesthetician and instructor with a passion for wellness, has over 34 years of experience in the skin care industry, ranging from spa owner, medical spa director, writer, and educator. She is the director of media education for BiON Research. Through a dedication and philosophy of creating beauty through skin health, McKowen has both a clinical and holistic background. Her expert knowledge stems from extensive and ongoing studies in cosmetic chemistry, massage therapy, aromatherapy, thallasotherapy, phytotherapy, health, and nutrition.