The most important objective of photoprotection must be to prevent rising rates for skin cancer and reduce health care expenditures for a largely preventable disease. It is now accepted that UV radiation is the main cause of photocarcinogenesis, photoaging and immune suppression. The risk of sunburn from UVB exposure has long been implicated as a major hazard to human skin. Recent studies support a more prominent role for UVA over UVB in genetic damage to the keratinocytes in the basal layer of the epidermis where most cancers occur. This basal layer shows more UVA than UVB fingerprint mutations, suggesting a primary role for UVA in human skin carcinogenesis. A contemporary view is that UVB causes direct DNA damage, whereas UVA results in direct DNA damage and indirect effects from ROS, photoimmunosuppression, and disruption of repair mechanisms. UVB initiates and modulates these harmful effects whereas UVA is responsible for widespread effects and completing the damage cycle. Photoprotection with traditional UVB biased sunscreens with little or no UVA protection must now be abandoned and a new clinical strategy adopted.
Rising cancer rates show that the current approach has failed and critical analysis argues that ineffective UVB biased sunscreens are an important contributory factor. A minority of the products available in Canada or the USA provide adequate protection against the deeper penetrating UVA-I (340-400nm). In North America > 80% of products claim or imply UVA absorption by labels such as “broad-spectrum or extra UVA protection” despite containing no effective UVA filters, particularly in the UVA-1 band. The Environmental Working Group (EWG) assessed over 1800 sunscreens and found that 90% had little or no UVA-I protection, despite a broad-spectrum label claim. Consumers are lured into assuming that they are being protected from the entire solar UV spectrum (290-400nm), and are distracted by high SPF numbers into mistakenly believing that their sunscreen is reducing all the risks of sun damage. Sunscreens that absorb mainly UVB denoted by the SPF number, reduce the risk of sunburn but may be detrimental by allowing you to stay out longer. You do not burn but you actually increase your risks from UVA injury – immune suppression, premature photoaging, and skin cancer. A few N. American sunscreens offer some UVA filtering but most fail to provide the minimum UVA protection required in Europe.
Health Canada and the FDA changed their regulations in 2011 to ensure that a broad spectrum claim was an accurate one. For decades, the SPF on a product’s label was the only measurement available to consumers to help make a decision about a sunscreen’s protective capabilities. SPF values indicate UVB and UVA-2 protection from 290 to 340 nm. There was an urgent need to enable the consumer to assess the UVA-1 protection afforded by a sunscreen like Europe and most other countries outside N. America. Both countries adopted the rule of the Critical Wavelength (CW) test. The CW can be assessed by a variety of in-vitro tests that plots an absorption curve and assesses the wavelength on the y-axis where 90% of the area of the curve falls under. If 90% of the curve falls on or after the 370 nm mark (the portion of UV light that is considered the longest wavelengths of UVA) then the sunscreen can be labeled ‘broad-spectrum’ under the new law. See Figure 1 for an example.
The Critical Wavelength Test does not by itself provide an accurate assessment of whether a sunscreen is broad spectrum. The following are some reasons why the test can be misleading:
- The test is a relative comparison of UVB vs. UVA, not a test of absolute
- The result of the test is affected largely by the shape of the curve.
Figure 2 (absorption curves) and Figure 3 (sunscreen actives and concentrations in comparison to CW result) shows how the CW sometimes fails to accurately describe the true protection profile of a sunscreen.
Figure 2: Absorption Curves of Four Brands
 Results from testing of actual products at an independent third party laboratory
Figure 3: Sunscreen Brands with their Actives and Critical Wavelength Result
|Formula||Curve Colour||Actives||Critical Wavelength Result|
|Every Morning Sun Whip SPF 25||Dark Blue||15% Zinc Oxide, 7.5% Encapsulated Octinoxate||362|
|Simply Zinc Whip Sun Whip SPF 30||Green||22% Zinc Oxide||370|
|Brand E SPF 45||Light Blue||9% Zinc Oxide, 7.5% Octinoxate||372|
|Brand C SPF 30||Light Red||1.9% Zinc Oxide, 3% Titanium Dioxide||376|
 SPF values are as reported on product labels, Critical Wavelength results are from testing of actual products at an independent third party laboratory
In Figure 2, the Green Curve offers the highest levels of protection through the full range of UVB and delivers excellent UVA protection. It represents our Simply Zinc Sun Whip SPF 30 with 22% zinc oxide as its only active ingredient. You can see that it offers the highest protection at every wavelength and is flat confirming that it delivers “balanced” protection – virtually equal protection at every wavelength in the UV band (290-400nm). Experts recommend that the ideal sunscreen must achieve this quality confirmed by an absorption curve that is high and flat. This product that gives the best photoprotection had a CW measured at 370 nm and barely passed the CW test. It can be labeled broad-spectrum, but based on CW would appear to be less protective than Brands E and C.
The other three curves compared to each other provide the best examples of the flawed nature of the CW test. The light pink curve, Brand C SPF 30, has the highest Critical Wavelength result of 376. It also has the lowest concentrations of actives at about 2% Zinc Oxide and 3% Titanium Dioxide. It has the lowest curve as expected, and offers the lowest amount of protection from 290 nm to 370 nm. It gets a high Critical Wavelength result because its curve is flat. Therefore, while it meets the criteria of being relatively flat it does not meet the criteria of being high. It gives uniformly poor protection at every wavelength from 290-370 nm and virtually none at 370-400 nm.
The Dark Blue (the Every Morning Sun Whip SPF 25 with 15% Zinc Oxide and 7.5% Encapsulated Octinoxate) vs. the Light Blue curve (Brand E SPF 45 with 9% Zinc Oxide and 7.5% Octinoxate) confirms that more Zinc Oxide is always a better thing. The Dark Blue curve (Every Morning Sun Whip SPF25) offers more protection at every point from 290-370 nm, despite a CW of 362 due to the shape of its curve. Its encapsulated octinoxate gives better UVB absorption than the regular octinoxate in Brand E. It fails the CW test but gives better protection than brand E that passes. The shape of the curve may erroneously negate the actual level of protection in some cases. More protection is obviously a good thing in real life. Yet it may shift the CW curve to the left and fail a sunscreen. To pass the arbitrary CW 370 nm standard, one could reduce the level of encapsulated octinoxate in Every Morning Sun Whip from 7.5% to 4% by flattening the curve and shifting the 90% crossover to the right. Less protection gets you a pass like many sunscreens that now make a label claim that is misleading or false.
The CW is used in Europe along with the SPF/UVA-PF ratio to show the consumer the actual level of UVA protection relative to the UVB level or SPF. The ratio has to exceed 1/3. This means that for a SPF 30 sunscreen UVA Protection Factor has to be > 10, for a SPF 60 product UVA-PF has to exceed 20. The CW is a second but less important metric that gives the “balance” of the broad-spectrum activity, once the first criteria is achieved, the higher the CW is above 370, the more UVA protection afforded. The CW alone is a flawed measure of UVA activity and the balance or broad-spectrum nature of the sunscreen. Professor Brian Diffey of Newcastle University who developed the test is the harshest critic of the FDA for adopting this test as the sole measure. There is expert consensus that using CW alone fails to ensure adequate UVA protection required for true broad spectrum coverage.
Dominique Moyal from L’Oreal Research & Innovation called attention to this issue in 2001. He presented photometric data from 2 sunscreens labeled “broad spectrum”, with SPF 15 and CW 370 nm. One had a UVA-PF of 2.4 and the other 10.4. The former would have a UVA index (SPF/UVA-PF ratio) of 0.16 a fail in the EU, the latter a UVA index of 0.66 showing balanced protection and pass in the EU. Both would now pass in N.America. He presented the data for 16 sunscreens with SPF values 15-60 and showed there was no linear correlation (the data scatter was wide) between CW and SPF/UVA-PF values. Furthermore, a CW ≥ 370 nm is not equivalent to a ratio UVA-PF/SPF ≥ 1/3 and a high SPF and CW > 370 nm doesn’t ensure a higher UVA protection than a lower SPF product with the same CW.
These curves are also instructive in relation to their labeled SPF. You’ll notice that within the UVB portion of the curve (from 280 nm to 320 nm), the highest curve is again our Simply Zinc Sun Whip SPF 30. Many sunscreens report an inflated SPF by manipulating the SPF test done on human volunteers. Anti-inflammatory or antioxidants that reduce the redness on skin falsely elevate the SPF result that depends on the degree of erythema or redness as read by an observer. The skin appears less red not by a true reduction in UV radiation but by masking the biologic endpoint that in real life warns you to get out of the sun. In-vitro SPF testing does not depend on the degree of erythema and cannot be rigged, and is being refined by The ISO, hopefully to become a global standard. From the absorption curves, there is no possible way that Brand E can have an SPF 45 when it has lower absorption in the entire UVB portion than Simply Zinc Sun Whip SPF 30 with the highest UVB absorption. Brand E labeled SPF 45 also has lower absorption in UVB than Every Morning Sun Whip SPF 25. Finally, Brand C (light pink curve) labeled SPF 30 cannot possibly have a true SPF 30 and be positioned considerably lower than our sunscreens at SPF 30 and SPF 25.
Consumers are once again left without a clear way of knowing the true protective qualities of a sunscreen. Products that do not pass the Critical Wavelength test of 370 nm must label their products as only protecting against sunburn and not skin cancer or photo-aging. Those that pass make a very specific claim that they aid in preventing cancer and photoaging. That may be entirely false and we have the contradiction that sunscreens not able to make the claim provide superior protection than those that do. The consumer is actually worse off than before. The broad-spectrum claim was somewhat generic and many consumers may not have appreciated its exact significance and that it was misleading. Now we have a very specific claim of protection against cancer and photoaging, which may still be misleading or untrue in many cases.
Consumers in N.America deserve an easy way of assessing their sunscreens but they also require an accurate one. The SPF/UVA-PF combined with the CW as required in Europe would have provided both. Industry lobbyists influenced the FDA to move away from this and a similar reliable standard- The Boots/Diffey Star Rating. Using either standard would have excluded the majority of our sunscreens that did not provide adequate UVA-1 or true broad spectrum protection. The use of the limited CW test alone allowed many deficient sunscreens to pass. We advise consumers to look at the active ingredients in a sunscreen for the best assessment. Currently in North America, Zinc Oxide is the best and safest broad-spectrum filter that protects against all UV bands, but the most efficiently against UVA rays. Consumers must remember the truism that the more zinc oxide -the better your reliable and actual protection.
- Zinc Oxide provides the most broad-spectrum protection and remains the best UV filter available in North America.
- More Zinc Oxide means more protection. Consumers should look for the protection afforded by levels at 15% or more approaching the allowable maximum of 25%, and expect protection to decrease the lower the concentration.
- Overall protection may be improved within the 15-25% range by adding other agents like titanium dioxide (UVB and some UVA-2 protection) or encapsulated octinoxate (UVB). Both are large molecules that remain within the outer dead layer of skin (stratum corneum), and like zinc oxide, they avoid the risks of soluble filters that are absorbed through the skin, such as hormone disruption, reproductive problems or cancers, and rarely photocontact skin allergy or irritation.
- The FDA and health Canada continue to deprive N. American consumers of access to the benefits of Tinosorb S™ and Tinosorb M™, two excellent broad-spectrum filters with good safety profiles according to the EWG, and widespread use across the globe for almost 15 years. Until they become available, zinc oxide is the safest and single most effective broad-spectrum filter available in N. America.
Sara Dudley and Dr. Denis Dudley