THE LABEL SPF CANNOT BE USED TO ESTIMATE SAFE SUN EXPOSURE TIME
Photo Credit: Adobe Stock Close-up of a sunburn marks on a woman's back File # 357594601
North American consumers should not rely on label claims - whether it is the SPF or claims of UVA and Broad spectrum protection. Most of our brand name sunscreens would not pass European or Australian criteria for UVA-PF (UVA- Protection Factor) and their better standards for Broad Spectrum coverage. Proper and adequate UVA protection may be the most essential property for a sunscreen to actually prevent skin cancer and photoaging. The global market, particularly in North America is dominated by UVB- BIASED sunscreens with inadequate UVA protection, despite label claims saying ‘BROAD SPECTRUM’ UVA/UVB. Even the EWG (Environmental Working Group) recognizes this reality in their 2017 Sunscreen Report. More on this in my next BLOG.
There are over 25 stakeholder and professional coalitions with Comprehensive Cancer Control (CCC) plans that publicise a prevention strategy. Language may differ but they all focus on key elements of sun avoidance, never burn or tan from UV exposure, wearing protective clothing with a tight weave, wear UV protective sunglasses, and generously apply a sunscreen with sun protection factor (SPF) 15 or higher and both UVA/UVB protection. Sunscreen use is the weakest link in the protocol. Rising cancer rates show that the current approach has failed and critical analysis argues that ineffective UVB-BIASED sunscreens dominating the N.American market are a driving factor. Australia where balanced sunscreens using better UVA filters are plenty, are actually seeing skin cancer rates levelling off or falling in certain provinces. Two landmark studies from Australia show that effective sunscreens applied daily can potentially reduce all forms of skin cancer. In N. America the grim reality is otherwise:
Skin cancer is now the most common cancer in the United States with the incidence essentially doubling for all skin cancers in 40 years, and they now account for more than 50% of all human cancers - i.e. skin cancer cases outnumber all other cancers combined.
In 2017, over 160,000 Americans are expected to be diagnosed with melanoma, which is the leading cause of cancer death in women ages 25-30 and the second leading cause in women ages 30-35. In ages 15-29, melanoma is the second most commonly diagnosed cancer. From 1970 to 2009, the incidence of melanoma increased by 8-fold among young women and 4-fold among young men. In the USA, one person dies of melanoma every 54 minutes (almost 10,000/year). 4000 Americans die in a year from Squamous Cell Cancer (SCC) .
Preventing sunburn (early effect) or UVA damage (early and late effects), and damage to the genetic and immune apparatus of the skin is the essence of effective photoprotection. The label SPF is supposed to quantify a sunscreen’s ability to prevent that early sign of sun damage. The SPF as measured by FDA and Health Canada mandated tests give a poor estimate of the sunscreen’s actual performance in sunlight.
The premise that SPF can be used to plan your exposure time is based on several invalid assumptions. Recent studies confirm that the lab or label SPF is inaccurate, when compared to the real life value obtained in sunlight. The lamp used in calculations for label purposes, only emits 290-400 nm based on the false assumption that the erythema reaction was mediated only by UVR (UVB and UVA). Visible Light (VL at 400-740 nm)) and Infra-red (IR at beyond 740 nm)) could be responsible for up to 20-30 % of the erythema response. Sunlight has more UVA (up to 5X ) than the testing lamp emission. Industry and physicians continue to advise consumers that the SPF can be used to calculate the safe exposure time for protected skin outdoors. We know differently - fair individuals mostly get sunburned with prolonged outdoor exposure or during tropical vacations, despite using high SPF sunscreens and stringently following all the re-application instructions. Media reports in 2015-2017 from Consumer Reports, the BBC in the UK, CBS, NBC, and CNN in the USA, have all presented data that up to 50% of brand name sunscreens fail to achieve even 50% of their labelled SPF values.
Science now confirms this travesty. The label SPF is inaccurate when compared to the real life value obtained in sunlight. A landmark study presented at the 26th Annual Meeting of The Photomedicine Society (Orlando, Florida, February 2017), showed that 50 commercially available sunscreens with label SPF 50 or more had SPF values of 6-10 when measured in sunlight (Hughes S. and Cole C.). No wonder, as testing lamp emission spectrum is far removed from that of actual terrestrial radiation, and the intensity used in testing is different from sunlight. The compliance factor also adds another real life problem as most users apply < than the 2 mg/cm2 as done for the lab test. Scientists also now provide the principles in physics that explain why the SPF test cannot be accurate (Diffey B, Osterwalder U, 2017). They report that labelled SPF, determined by in vivo assay using a UV solar simulator, overestimates the SPF that would be expected in natural sunlight. Products labelled SPF50+ may not be able to achieve a protection against sunlight of more than 25-fold., or SPF 25. The popular interpretation of the SPF to mean how much longer skin covered with sunscreen takes to burn in sunlight compared with unprotected skin, can no longer be defended.
Any falsely high SPF reading can be further manipulated by adding anti-redness agents (similar to aspirin) that artificially increases the MED (Minimal Erythema Dose) used to determine the SPF, for the sunscreen containing these anti-inflammatory chemicals. Sunscreens are replete with SPF boosters- bisabolol, niacinamide, salicylate compounds, and numerous others. This may be very harmful to a consumer. The false (often high SPF 50-100) values distort the reality of what protection to expect. If you are very fair – Type 1- always burns never tans- you may actually burn within 5 minutes with extreme sun exposure. An SPF 30 conveys the impression that it is safe to stay out for up to 150 minutes and SPF 50 for up to 250 minutes. A real life SPF 10 in sunlight means you should multiply your 5 minute burn time by only 10 for a safe 50 minute exposure, then get out the sun or re-apply your sunscreen liberally if you stay out longer. A boosted SPF is falsely elevated by interfering with the biologic endpoint or early warning signal of redness, the first sign of sunburn. It is no longer commensurate to the amount of radiation being prevented from reaching your skin, but related to delayed redness. You are actually burning but have no way of knowing this as your early warning signal has been blunted. This false sense of security may make you remain outdoors i/o seeking shade. You will experience more sun damage and incur the risks of skin cancer and photoaging. This is only related to UVB exposure - think of the damage resulting from the more harmful UVA radiation that you are now receiving in high levels, particularly since most N. American sunscreens have inadequate UVA-PF values.
Use no more than half the label SPF when calculating your outdoor exposure time, and if you are redhead or extremely fair use a factor of 10.
It is better to use the other elements of a photoprotection strategy – avoid sun exposure, wear UV protective clothing, wear head gear and UV protective sunglasses etc. - to the extent you can, and use a sunscreen with a safe UVA filter like zinc oxide in adequate concentrations.
The particle type sunscreens that use zinc oxide, titanium dioxide, encapsulated octinoxate, drometrizole trisiloxane (Mexoryl XL™), terephthalylidene dicamphor sulfonic acid (Ecamsule or Mexoryl SX™), biscotrizole (MBBT or Tinosorb M™), bemotrizinol (BEMT or Tinosorb S™), and others are large in size, sit on the skin avoiding any entry into blood and the various attendant risks. Only the first five are available in Canada. Mexoryl XL™ and SX™ are patented to L’Oreal and regrettably are usually combined with undesirable soluble hydrocarbon filters, which should be stringently avoided. All except titanium dioxide and encapsulated octinoxate are UVA filters, and when mixed with other safe UVB filters achieve dispersions of spectral homeostasis (balanced UVA/UVB protection). In this situation where a sunscreen behaves like a neutral density filter, the label SPF may be closer to the Real Life SPF value in sunlight. Look for products that have > 20% zinc oxide alone, or 15 % with 7.5% titanium dioxide or encapsulated octinoxate.
For maximum protection and to avoid all the controversy on hormone disruption and environmental hazards, use only sunscreens with particle based or large molecular weight filters in the right combination. The high UVA protection achieves that flat balanced protection where the ratio UVA-PF/SPF approaches 1, and the label SPF comes closer to the Real Life value in sunlight. Strictly avoid all small molecular weight soluble hydrocarbon filters – avobenzone, oxybenzone, homosalate, octisalate, octocrylene, regular octinoxate, and 4-methylbenzilidene camphor. All may enter blood and only avobenzone has any UVA attenuation. It still gives a significant UVB bias where up to 30% of UVA between 340-400 nm – the most damaging UV rays are transmitted to your skin.
© Denis K. Dudley MD, October 2017. All rights reserved.