Full Transcript Sunscreen and Skin Cancer Evidence 0:10 Decades ago, studies started bubbling up reporting that not only was the use of 0:14 sunscreen not found to be protective against skin cancer, but it was 0:17 associated with significantly elevated risk. But, subsequent studies offered 0:22 the obvious explanation of this paradox. People who use sunscreen are more likely 0:27 to be sunbathers. That's like finding those who use 0:30 motorcycle helmets are more likely to die in the highway. I mean, it's not 0:34 that sunscreen and helmets aren't protective, it's just that they're 0:36 associated with engagement in risky activities. But, you don't know until 0:42 you put it to the test. As I noted in my last video, randomized controlled trials 0:46 have shown that regular use of sunscreen can arrest visible signs of skin aging, 0:51 including biopsy-proven reductions in UV-related skin damage. But, are there 0:55 interventional trials proving sunscreen can prevent cancer? Yes. 1:01 Organ transplant recipients are highly susceptible to skin cancers because they 1:04 have to be given immune suppressants to prevent organ rejection. A group of 120 1:10 organ recipients were equally informed about sun protection measures, but half 1:14 were given free broad-spectrum SPF 50+ sunscreen for daily application to their 1:19 head, neck, forearms, and hands. After 2 years, there were nine new basal cell 1:23 carcinomas in the control group versus only two in the sunscreen group. That 1:27 sounds good, but it may have just been a fluke. In contrast, there was a highly 1:31 significant difference in the proportion of patients who got new invasive
Clinical Trials in High-Risk Patients 1:34 squamous cell carcinoma. Eight new cases in the control group versus zero in the 1:39 sunscreen group. But, wait until you hear about what 1:43 happened to their actinic keratoses, the precancerous growths that can turn into 1:48 skin cancer. They all started out covered in them. A total of 191 detected 1:54 in each group. In the subsequent 24 months, the control group developed 82 1:58 new ones. How many did the sunscreen group develop? -102. 2:05 More than 100 pre-cancerous growths in the sunscreen group spontaneously 2:10 regressed and vanished completely compared to 82 new growths developing in 2:15 the control group without a single one disappearing. 2:17 Their bodies, even in their immunocompromised state, could heal 2:21 itself once it just stopped being bombarded with so many cancer-causing 2:26 rays. Other randomized control trials have 2:28 shown similar findings. But generalizability is limited. The 2:33 studies all used high-risk populations. For example, those living in subtropical 2:37 climates or with a personal history of pre-cancerous lesions. So, cancer 2:41 prevention efficacy in the general population would be expected to be less. 2:46 On the other hand, the studies could also have underestimated the impact 2:49 since they were relatively short-term, not exceeding 4 years, and ethically had 2:54 to allow the control group participants to slather on their own sunscreen, which 2:58 would dilute the difference between groups. 3:01 For maximum effectiveness, sunscreen needs to be applied properly, which 3:05 apparently rarely happens in the real world. In a study of nearly 5,000 skiers 3:10 and snowboarders, almost no one, only about 4%, were fully compliant with 3:15 sunscreen recommendations. First, there's the amount. The FDA standard is 3:20 2 mg per square centimeter. What does that mean? Use the teaspoon rule. One
How to Apply Sunscreen Correctly 3:26 teaspoon for your face, head, and neck. One for the front of your torso, another 3:30 for your back, one teaspoon for each arm, and two teaspoons for each leg. 3:34 That's a total of nine teaspoons. It's about the total volume equivalent of a 3:38 golf ball or or a shot glass to help you visualize it. 3:43 Unfortunately, the average sunscreen user may only apply a quarter of the 3:46 recommended amount. This is why high SPF sunscreens are often recommended, like, 3:51 you know, 50+ SPF. Although the FDA recommends a minimum SPF of only 15 to 3:56 prevent skin cancer under normal consumer conditions, even an SPF of 50 4:01 may effectively give you only an SPF of 12.5 because most people don't put on 4:06 enough. Randomized, double-blind, head-to-head, 4:09 split-face experiments where you're randomized to apply one sunscreen to one 4:13 side of your face and another sunscreen to the other side show that in real-life 4:17 use, SPF 100-plus sunscreen works significantly better than SPF 50-plus 4:23 sunscreen. More than 50% of the participants were sunburned more on 4:27 their SPF 50-plus side compared to only about 5% on their SPF 100-plus side. 4:34 Now, potential downside of higher SPF sunscreens is that they could provide a 4:38 false sense of security. Those randomized with SPF 30 sunscreen ended 4:42 up spending more cumulative time in the sun than those who receiving an SPF 10 4:46 sunscreen, [clears throat] as much as five times longer in some cases. 4:50 Uh, what else? Well, people tend to remember to use sunscreen on a sunny day 4:54 at the beach, but sun protection is needed even on cloudy days since the UV 4:58 rays are not dampened as much as visible light. There's even a phenomenon known 5:02 as cloud enhancement, where overcast skies can sometimes result in even more 5:07 UV reaching the Earth's surface compared to clear skies. Sunscreen labels often 5:11 suggest waiting at least 15 minutes after application before going outdoors, 5:15 uh, but when put to the test, sunscreen was found to start working immediately 5:19 with the full effect apparent by minute 10. However, if water resistance is 5:23 required, it may be prudent to wait the full 15 to 30 minutes after application 5:27 before taking a dip. The terms waterproof or sweatproof 5:32 appear to be meaningless marketing as no difference in retention was noted 5:35 between {quote} waterproof products and those that were merely labeled water 5:40 resistant. Both were better than non-water resistant products, though,
SPF, Reapplication, and Product Types 5:43 which lost nearly all their protective effects within 20 minutes of water 5:48 immersion. The suggestion that sunscreen should be 5:51 reapplied every 2 to 3 hours only applies under conditions in which it is 5:55 rinsed off by water or sweat or rubbed off by friction from clothing or sand. 5:59 Even after allowing sunscreen to dry first for 20 minutes, between 15 and 60% 6:05 of its protective effect can be lost after contact with sand. 6:09 Otherwise, if the recommended amount is applied and the sunscreen layer is not 6:12 disturbed, SPF can be maintained for as long as 8 hours. 6:18 What kind of sunscreen should you use? Cream-based is preferable to spray-on 6:22 since the completeness of application is more readily visualized. 6:26 To help with adequate coverage, spray-on sunscreen should be rubbed on 6:29 immediately after spraying. Aerosolized sunscreens are flammable and 6:34 can combust on skin upon exposure to an open flame even after the sunscreen has 6:38 dried. What's more, the safety of breathing in 6:41 aerosolized sunscreen chemicals has not been adequately studied. Though frankly, 6:46 the same thing could be said about rubbing them on your skin. 6:50 The concerns surrounding sunscreen safety are threefold. 6:53 Increased intentional sun exposure, vitamin D deficiency, and untoward 6:58 effects from systemic absorption of sunscreen chemicals. 7:02 In the 1800s, we first learned that UVB caused sunburns and formulated 7:07 sunscreens to block it. Nearly a century later, we learned about the contribution 7:11 of UVA. Now, a full century later, we are realizing that infrared and visible 7:16 light may also be contributing cancer and premature skin aging. 7:20 Sunlight comes to us in three major bands: visible light, 7:23 ultraviolet, and infrared. Visible light includes the colors of the rainbow, red, 7:29 orange, yellow, green, blue, indigo, and violet, or ROYGBIV. 7:33 Ultraviolet, UV, is to the right of violet in ROYGBIV, and infrared to the 7:38 left of red. Sunscreen can protect us against the free radical damage of UV, 7:44 but half of the free radical formation in our skin from the sun may be from the 7:47 visible or infrared spectrums which sunscreens may not adequately cover. So,
Safety, UV Bands, and Mineral Sunscreens 7:52 that's where sun avoidance strategies come in. But, you can imagine how shade 7:58 seeking could be undermined by the solacement of a sunscreen security 8:02 blanket. What about vitamin D? The theoretical concern about sunscreen 8:07 affecting vitamin D status does not seem to manifest in the real world, likely 8:11 because the UV dose necessary for vitamin D production is so low well 8:15 before skin turns a pinker shade. However, concerns about the systemic 8:22 absorption of sunscreen chemicals were underscored by the recent FDA bombshell 8:27 that not a single one of sunscreen chemicals in current use can be 8:31 considered generally recognized as safe. Only two active ingredients got the 8:36 green light. The two non-chemical mineral sunscreens, titanium dioxide and 8:40 zinc oxide. The regulation was based on a growing 8:44 body of evidence that transdermal, meaning through the skin absorption of 8:47 sunscreen chemicals was greater than we previously thought, raising unevaluated 8:53 safety concerns. Unevaluated because we previously didn't think so much got into 8:57 our bloodstreams. In 2019, a study published in the Journal of the American 9:02 Medical Association found that under maximum usage conditions over a period 9:05 of days, the blood levels of all the sunscreen chemicals they tested exceeded 9:09 the FDA threshold that could potentially waive further safety testing. Then in 9:14 2020, they found that just a single application of all the chemical 9:18 sunscreens they tested surpassed the threshold. Now, just because they're 9:22 absorbed into our system doesn't necessarily mean they're unsafe, it just 9:26 means they need to be tested for safety, which the FDA determined the 9:30 multi-billion dollar sunscreen industry has so far failed to do. 9:35 The FDA concluded that two ingredients can be considered safe, zinc oxide and 9:39 titanium dioxide. And two can be considered unsafe, PABA and trolamine 9:45 salicylate. And the other 12 ingredients that are 9:48 currently marketed have yet to be sufficiently safety tested. 9:52 According to a review of more than 700 sunscreen brands, it appears PABA and 9:56 trolamine are no longer being marketed in sunscreen sold in the United States, 10:00 uh but they still may be available in other countries. 10:03 Until the data are in on the rest of the chemical sunscreens, I would recommend 10:06 sticking to the two mineral sunscreens. Historically, they've tended to be
Sunscreen Use and Skin Cancer in Darker Skin 10:11 thicker and whiter, which could lead to even more severe underdosing, but newer 10:15 micronized formulations with smaller mineral particle sizes tend to be less 10:20 noticeable. This is particularly an issue for those 10:23 with darker skin. Uh the average built-in SPF of black skin, also known 10:27 in the medical literature as {quote} ethnic skin or 10:31 SOC, skin of color, is about 13 naturally, compared with 10:36 only about three for white skin. Though there haven't been any interventional 10:40 studies on sunscreen effectiveness for skin cancer prevention in people 10:43 [clears throat] with dark skin, an SPF of 13 is not considered sufficient sun 10:48 protection. So, the American Academy of Dermatology recommends regular sunscreen 10:52 use with an SPF of 30 or higher for people of all skin types. 10:57 Unfortunately, only about 12% of non-Hispanic blacks and 31% of Hispanics 11:01 report regularly using sunscreen, compared about 44% of non-Hispanic 11:05 whites. Uh despite this, the incidence of melanoma, the deadliest skin cancer, 11:10 is five times lower in Hispanics compared to whites and more than 25 11:13 times lower among blacks. However, the mortality rate, if you do get it, is 11:18 higher among African Americans, presumed to be due from delayed diagnosis. 11:49 >> Oh.
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