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As of 2:19 p.m. EST today, it is officially autumn in the Northern Hemisphere. Pumpkin patches and apple orchards will replace trips to the beach, bathing suits will be tucked away, and the sun will start to set earlier. But one part of your summer routine should stay part of your daily life: sunscreen. Protecting your skin from the sun’s ultraviolet (UV) light is important all year round. To monitor your risk level, you can use the UV Index………Continue reading….
By: Laura Baisas
Source: Popular Science
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Critics:
Sunscreen use can help prevent melanoma and squamous cell carcinoma, two types of skin cancer. There is little evidence that it is effective in preventing basal cell carcinoma. A 2013 study concluded that the diligent, everyday application of sunscreen could slow or temporarily prevent the development of wrinkles and sagging skin. The study involved 900 white people in Australia and required some of them to apply a broad-spectrum sunscreen every day for four and a half years.
It found that people who did so had noticeably more resilient and smoother skin than those assigned to continue their usual practices. A study on 32 subjects showed that daily use of sunscreen (SPF 30) reversed photoaging of the skin within 12 weeks and the amelioration continued until the end of the investigation period of one year. Sunscreen is inherently anti-aging as the sun is the number-one cause of premature aging; it therefore may slow or temporarily prevent the development of wrinkles, dark spots and sagging skin.
Minimizing UV damage is especially important for children and light-skinned individuals and those who have sun sensitivity for medical reasons, including medical use of retinoids. In February 2019, the US Food and Drug Administration (FDA) started classifying already approved UV filter molecules into three categories: those which are generally recognized as safe and effective (GRASE), those which are non-GRASE due to safety issues, and those requiring further evaluation.
As of 2021, only zinc oxide and titanium dioxide are recognized as GRASE. Two previously approved UV filters, para-aminobenzoic acid (PABA) and trolamine salicylate, were banned in 2021 due to safety concerns. The remaining FDA-approved active ingredients were put in the third category as their manufacturers have yet to produce sufficient safety data — Pending further safety data, several FDA-approved active ingredients remain under evaluation.
Some researchers argue that the risk of sun-induced skin cancer outweighs concerns about toxicity and mutagenicity, although environmentalists say this ignores “ample safer alternatives available on the market containing the active ingredient minerals zinc oxide or titanium dioxide”, which are also safer for the environment. Regulators can investigate and ban UV filters over safety concerns (such as PABA), which can result in withdrawal of products from the consumer market.
Regulators such as the TGA and the FDA have also been concerned with recent reports of contamination in sunscreen products with known possible human carcinogens such as benzene and benzophenone. Independent laboratory testing carried out by Valisure found benzene contamination in 27% of the sunscreens they tested, with some batches having up to triple the FDA’s conditionally restricted limit of 2 parts per million (ppm). This resulted in a voluntary recall by some major sunscreen brands that were implicated in the testing, as such, regulators also help publicise and coordinate these voluntary recalls.
V.O.C.s (Volatile Organic Compounds) such as benzene, are particularly harmful in sunscreen formulations as many active and inactive ingredients can increase permeation across the skin. Butane, which is used as a propellant in spray sunscreens, has been found to have benzene impurities from the refinement process. There is a risk of an allergic reaction to sunscreen for some individuals, as “Typical allergic contact dermatitis may occur in individuals allergic to any of the ingredients that are found in sunscreen products or cosmetic preparations that have a sunscreen component.
The rash can occur anywhere on the body where the substance has been applied and sometimes may spread to unexpected sites.” There are some concerns about potential vitamin D deficiency arising from prolonged use of sunscreen. The typical use of sunscreen does not usually result in vitamin D deficiency; however, extensive usage may. Sunscreen prevents ultraviolet light from reaching the skin, and even moderate protection can substantially reduce vitamin D synthesis.
However, adequate amounts of vitamin D can be obtained via diet or supplements. Vitamin D overdose is impossible from UV exposure due to an equilibrium the skin reaches in which vitamin D degrades as quickly as it is created. High-SPF sunscreens filter out most UVB radiation, which triggers vitamin D production in the skin. However, clinical studies show that regular sunscreen use does not lead to vitamin D deficiency . Even high-SPF sunscreens allow a small amount of UVB to reach the skin, sufficient for vitamin D synthesis.
Additionally, brief, unprotected sun exposure can produce ample vitamin D, but this exposure also risks significant DNA damage and skin cancer. To avoid these risks, vitamin D can be obtained safely through diet and supplements. Foods like fatty fish, fortified milk, and orange juice, along with supplements, provide necessary vitamin D without harmful sun exposure. Studies have shown that sunscreen with a high UVA protection factor enabled significantly higher vitamin D synthesis than a low UVA protection factor sunscreen, likely because it allows more UVB transmission.
The sun protection factor (SPF rating, introduced in 1974) is a measure of the fraction of sunburn-producing UV rays that reach the skin. For example, “SPF 15” means that 1⁄15 of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter (mg/cm2). It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed, usually every two hours.
The SPF is an imperfect measure of skin damage because invisible damage and skin malignant melanomas are also caused by ultraviolet A (UVA, wavelengths 315–400 or 320–400 nm), which does not primarily cause reddening or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad-spectrum sunscreens are designed to protect against both UVB and UVA.
According to a 2004 study, UVA also causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas. Even some products labeled “broad-spectrum UVA/UVB protection” have not always provided good protection against UVA rays. Titanium dioxide probably gives good protection but does not completely cover the UVA spectrum, with early 2000s research suggesting that zinc oxide is superior to titanium dioxide at wavelengths 340–380 nm.
Owing to consumer confusion over the real degree and duration of protection offered, labelling restrictions are enforced in several countries. In the EU, sunscreen labels can only go up to SPF 50+ (initially listed as 30 but soon revised to 50). Australia’s Therapeutic Goods Administration increased the upper limit to 50+ in 2012. In its 2007 and 2011 draft rules, the US Food and Drug Administration (FDA) proposed a maximum SPF label of 50, to limit unrealistic claims. (As of August 2019, the FDA has not adopted the SPF 50 limit.)
Others have proposed restricting the active ingredients to an SPF of no more than 50, due to lack of evidence that higher dosages provide more meaningful protection. Different sunscreen ingredients have different effectiveness against UVA and UVB. The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an in vivo test is required by the FDA.
It can also be measured in vitro with the help of a specially designed spectrometer. In this case, the actual transmittance of the sunscreen is measured, along with the degradation of the product due to being exposed to sunlight. In this case, the transmittance of the sunscreen must be measured over all wavelengths in sunlight’s UVB–UVA range (290–400 nm), along with a table of how effective various wavelengths are in causing sunburn (the erythemal action spectrum) and the standard intensity spectrum of sunlight (see the figure).
Such in vitro measurements agree very well with in vivo measurements. Numerous methods have been devised for evaluation of UVA and UVB protection. The most-reliable spectrophotochemical methods eliminate the subjective nature of grading erythema. The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring sunburn protection.
Originally developed in Japan, it is the preferred method used by manufacturers such as L’Oréal. Instead of measuring erythema, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an in vivo test like SPF.
In addition, the European Cosmetic and Perfumery Association (Colipa) has introduced a method that, it is claimed, can measure this in vitro and provide parity with the PPD method. Sunscreen formulations contain UV absorbing compounds (the active ingredients) dissolved or dispersed in a mixture of other ingredients, such as water, oils, moisturizers, and antioxidants. The UV filters can be either:
- Organic compounds which absorb ultraviolet light. Some organic compounds (bisoctrizole and phenylene bis-diphenyltriazine) also partially reflect incident light. These are also referred to as “chemical” UV filters.
- Inorganic compounds (zinc oxide and titanium dioxide), which reflect, scatter, and absorb UV light. These are also referred to as “mineral” filters.
The organic compounds used as UV filter are often aromatic molecules conjugated with carbonyl groups. This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin. So, upon exposure to UV light, most of the ingredients (with the notable exception of avobenzone) do not undergo significant chemical change, allowing these ingredients to retain the UV-absorbing potency without significant photodegradation.
A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown. The stability of avobenzone can also be improved by bemotrizinol, octocrylene and various other photostabilisers. Most organic compounds in sunscreens slowly degrade and become less effective over the course of several years even if stored properly, resulting in the expiration dates calculated for the product.
Sunscreening agents are used in some hair care products such as shampoos, conditioners and styling agents to protect against protein degradation and color loss. Currently, benzophenone-4 and ethylhexyl methoxycinnamate are the two sunscreens most commonly used in hair products. The common sunscreens used on skin are rarely used for hair products due to their texture and weight effects.
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