Thursday, October 1, 2015

Into The Fire: Sun Protection From A To B

In the last month, Jessica Alba has made splashes across media headlines, but not for her latest role in a Hollywood blockbuster. The Honest Company, which she founded in 2011, has been charged with two lawsuits filed by consumers. Both lawsuits cite ineffective sun protection by the Honest Company sunscreen, and countless online images of sunburned children and adults appear to support these allegations. The failure of the sunscreen highlights a need for better education regarding sunscreen use and sun exposure. So let’s start with the one currently under fire.

Jessica Alba’s recent role has been protecting everyday people from allegedly harmful chemicals found in standard household products and cosmetics; her Honest Company offers “all natural” substitutes.
The Honest Company sunscreen contains only one active ingredient, zinc oxide, a naturally occurring mineral known for its UV reflecting properties. (The second lawsuit cites false advertisement for claims of using only “natural” substances when apparently synthetic components were included. And although zinc oxide exists naturally as zincite, it is likely that the zinc oxide used in sunscreen is synthesized in the lab). Zinc oxide is an effective broad-spectrum sunblock, protecting against both UVA and UVB radiation, but adequate concentrations must be used. If you’ve ever felt like your sunscreen just wouldn’t rub in, you’ve likely used zinc oxide, as its large particles leave a white, opaque residue many sunscreen users dislike.

The Hoff boasted, “Beyond its entertainment values, 'Baywatch' has enriched and in many cases helped save lives.” Perhaps he was referring to the prevention of nose-specific skin cancer, as he may have inspired others to liberally, but very specifically, apply chalky zinc oxide sunscreen to this body part.
Indeed, last year, the Honest Company sunscreen contained 20% zinc oxide, and many consumers complained of the undesirable aesthetic characteristics. This year, the Honest Company more than halved the zinc oxide concentration, reducing it to 9.3%. Although this change may have improved the sunscreen’s aesthetic properties, it most certainly reduced its ability to effectively block the sun’s UV radiation.

Zinc oxide, and its cousin, titanium dioxide, comprise inorganic sunscreen components. These particles reflect most of the radiation, but can absorb some of the energy. Newer sunscreen formulations typically use the nanoparticle version of these components, reducing the pasty appearance produced by the older, larger particles. Many sunscreens mix these minerals with the other class of sunscreen components:  organic molecules. Organic in this sense means “carbon-containing”, and refers to synthetic molecules made of carbon backbones. In addition to the inorganic components, some organic sunscreen molecules also provide broad-spectrum protection. However, the chemical structure of other molecules absorbs narrower wavelengths, so these are more effective when mixed with other narrow-spectrum or broad spectrum ingredients. The goal of mixing sunscreen components is to provide a broad-spectrum, photo-stable sunscreen that has acceptable aesthetic properties and increases the safety and effectiveness of the sunscreen.

These compounds are the most commonly used sunscreen ingredients. Avobenzone, ecamsules, and anthrilates absorb UVA radiation. Homosalate, octisalate, and octinoxate (also known as octyl methoxycinnamate) absorb UVB rays. Oxybenzone, octocrylene, and the inorganic particles zinc oxide and titanium dioxide filter both UVA and UVB radiation. Most sunscreens use a combination of these components to provide adequate broad-spectrum UV protection.
Forbes’ contributor David Korr noted that perhaps the formulation contributed to the sunscreen failure. The sunscreen label directed users to shake well before using, likely to redistribute to zinc oxide particles throughout the lotion. However, it is possible that many people skipped this step, resulting in some very heavy and greasy applications and other light and useless applications. So, formulation and proper consumer use indeed influence the effectiveness of sunscreen.
Other common misuses of sunscreen are applying too little or failing to reapply often enough. The FDA tests sunscreen at 2.0-2.2 mg of sunscreen per square centimeter of skin. To adequately cover an entire average-sized adult human body, at least 1.0 ounce (2 tablespoons or the volume of a shot glass), is needed.
In 2011, the FDA mandated higher standards for sunscreen labeling, requiring full compliance by the end of 2012. Under the new regulations, only sunscreens containing ingredients that absorb both UVA and UVB radiation can be classified as “broad-spectrum”. A sunscreen product with SPF (Sun Protection Factor) 15 or greater can state that it protects against all forms of sun damage, including sunburn, premature skin aging, and skin cancer. Those with SPF 2-14 can only state that they have been shown to prevent sunburn. Additionally, “waterproof” can no longer be used; rather if appropriate, labels can specify “water-resistant” with the length of time (either 40 or 80 minutes) before reapplication is needed. Keep in mind that these changes did not remove other sunscreens from the market, but merely mandated what they can claim.
Avoiding painful sunburns requires proper use of sunscreen—most importantly, actually using sunscreen whenever you are exposed to the sun for extended periods of time.
SPF refers to the amount of UV radiation filtered out by the sunscreen. Thus, a sunscreen user with a proper application of SPF 15 sunscreen is exposed to 1/15th of the sun’s harmful radiation. This suggests that SPF 15 sunscreen imparts a 15-fold increase in the length of time one can spend in the sun without getting burned. However, the FDA and Mayo Clinic recommend reapplying sunscreen at least every 2 hours and more often if swimming, sweating, or toweling off. Another way SPF is explained is that SPF 15, 30, and 50 protect from 93%, 97%, and 98% of UV radiation, respectively. Keep in mind that SPF refers to protection against only UVB radiation; there is no numerical rating of UVA protection.

UV radiation is more energetic than visible light, but not as energetic as X-rays; thus, it penetrates the top layers of skin, but not beyond that.
It was previously thought that UVA radiation was harmless; however, recent evidence shows that UVA does indeed contribute to tanning/sunburn, premature skin aging, and skin cancer. UVA comprises 90-99% of the UV radiation that reaches the Earth’s surface, whereas UVB radiation accounts for 1-10%. The stratospheric ozone layer filters out most of UVB and all of UVC radiation. The longer wavelength, lower energy UVA radiation can penetrate clouds, glass, and the skin’s dermal layer. Shorter, higher energy UVB rays do not significantly penetrate glass, but penetrate the epidermis and cause the majority of sun-induced skin damage.

UVA rays can penetrate deeper into the skin, reaching the dermis layer, whereas UVB penetration is limited to the epidermis.
The recent changes in sunscreen labeling were prompted primarily by new information on UVA radiation and the increasing incidence rates of skin cancer. In a future article, I will discuss how UV radiation promotes or causes skin cancer. Until then, remember that the highest concentration of UV radiation is 10 am – 4 pm, April through October. But that doesn’t mean you shouldn’t take precautions at other times of day or other times throughout the year. Sun protection should be a year-round commitment, keeping in mind that water, snow, and concrete can reflect sunlight. In addition to properly using sunscreen, wearing protective clothing and avoiding peak sunlight will protect your skin from UV radiation.

Contributed by: Julia van Rensburg, Ph.D.
Shah P, & He YY (2015). Molecular regulation of UV-induced DNA repair. Photochemistry and photobiology, 91 (2), 254-64 PMID: 25534312

Narayanan DL, Saladi RN, & Fox JL (2010). Ultraviolet radiation and skin cancer. International journal of dermatology, 49 (9), 978-86 PMID: 20883261

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