Hi {{first name | there}},

I've been sunscreen obsessed since I was a teenager. It may have been the first preventive-health decision I ever made, long before I knew what ApoB was or cared about VO2 max.

That being said, I'm here to tell you: there is no such thing as sunblock.

Why? In 2011, the FDA banned the words "sunblock," "waterproof," and "sweatproof" from sunscreen labels because they're false. No product blocks all sun. Nothing is waterproof. The most common word we use for sunscreen is misleading.

"Sunblock" implies a force field: apply once, become invincible. What you're actually applying is a thin protective film, tested in a lab at a precise dose (2 mg per square centimeter of skin) that almost nobody achieves in real life, and measured primarily against one outcome: how long it takes your skin to turn red.

Once you see sunscreen as a system with failure modes rather than a shield, choosing it gets much easier. The interesting question is not "mineral or chemical?" It is: what light are you trying to block, what skin problem are you trying to prevent, and will you actually reapply?

Sunscreen is one of the best-evidenced preventive interventions in dermatology, and as a longevity doctor, I am a big fan.

The landmark data comes from the Nambour trial in Queensland, which randomized 1,621 adults to daily SPF 15+ sunscreen versus use-it-when-you-feel-like-it. Daily application reduced squamous cell carcinoma tumor counts over 4.5 years. Ten years later, the daily-sunscreen group had half as many melanomas, and about a quarter as many invasive melanomas as the discretionary group. Caveat: melanoma was a secondary endpoint with small event counts (11 vs 22), so I'd call that evidence suggestive, not settled. But the direction is consistent, and invasive-melanoma truly harms longevity.

And for those of you who care about the aesthetic side of longevity (let's be real, most of us), the same trial population showed daily sunscreen users had 24% less measurable skin aging over 4.5 years, assessed by skin surface microtopography in adults under 55.

So the intervention works. The problem is that the label tells you almost nothing about which parts of the job a given product actually does.

SPF measures protection against erythema, sunburn, which is driven primarily by UVB. It is a burn timer. Products can also carry broad-spectrum testing, but the SPF number itself is not a photoaging score, a pigment score, or a total protection score.

It's about as useful for skin health as a biological age "score" is for your longevity health 😆 (which is to say, a little useful but definitely just one dimension).

Here's what your skin is actually exposed to, and where SPF does and doesn't help:

UVB. B = Burns you. Directly damages DNA. This is what SPF measures. Largely filtered by most glass, and is strongest midday and in summer.

UVA. A = Aging. Longer wavelength, penetrates deeper, present all year, and passes through most window glass (glass varies, but assume it gets in). It's a workhorse of photoaging, pigmentation, oxidative damage, immune suppression, and carcinogenesis. Your SPF number tells you nothing directly about UVA coverage. In the U.S., "broad spectrum" means the product passes a critical wavelength threshold of 370 nm: a pass/fail bar, not a graded score.

Europe requires UVA protection of at least one-third the labeled SPF; Asia uses PA ratings. The U.S. label gives you almost no info in comparison. A 2022 lab analysis of 51 U.S. sunscreens found that while 94% passed the FDA broad-spectrum test, only 35% would meet the EU standard, and measured UVA protection averaged roughly a quarter of the labeled SPF. (That study came from EWG-affiliated authors using in vitro methods, so I read it as a critique of our standards and product variability, not proof that every label is useless.)

Visible light. The piece almost nobody talks about, and the most useful thing in this issue for most people. Ordinary, see-it-with-your-eyes light can induce pigmentation, especially in darker skin tones and melasma-prone skin. And here's the kicker: standard UV filters, mineral or chemical, do not meaningfully stop visible light. A transparent SPF 50 can be excellent against UV and nearly useless against the wavelengths driving your melasma.

What does work: pigment. (This makes sense if you think about it; you need visible blockers to block visible spectrum light.) Tinted sunscreens containing iron oxides physically attenuate visible light.

In randomized trials in melasma, UV-plus-visible-light protection outperformed UV-only sunscreen and reduced relapse, with the evidence base continuing to strengthen. If you have melasma, post-inflammatory hyperpigmentation, or deeper skin tone that pigments easily, the tint is a big part of the treatment. This single detail changes more clinical outcomes in my pigment-prone patients (including myself!) than any SPF number.

Water and sweat. "Water resistant (40 minutes)" or "(80 minutes)" is a tested claim. "Waterproof" is a banned lie. The film washes off, rubs off, and sweats off, which is why reapplication is so important.

Dose. The lab tests sunscreen at 2 mg/cm². Real humans typically apply a quarter to a half of that, and protection falls off disproportionately when you underdose. Practically: about one ounce, a full shot glass, for an adult body, applied 15 minutes before exposure, reapplied at least every two hours and after swimming or heavy sweating.

The chronically forgotten spots: ears, lips, back of the neck, hands, tops of feet, hairline, and the scalp part. Sprays are fine if you spray until the skin glistens and rub it in (and don't inhale it, and don't stand near flame; yes, really). Powder and mist SPFs are touch-up tools for midday reapplication over makeup, not a beach strategy.

Put this all together and you get a clearer picture:

Most influencers and headlines say either "chemical sunscreens are poison" or "there's nothing to see." The truth is, as you might expect, a lot more nuanced.

In 2019 and 2020, FDA scientists ran maximal-use trials and showed that several common organic filters (avobenzone, oxybenzone, octocrylene, homosalate, octisalate, octinoxate) are absorbed into the bloodstream above the FDA's 0.5 ng/mL threshold.

The threshold is a trigger for more toxicology data, not a threshold for actual harm. Crossing it means "we need to study this properly," not "this is hurting you."

That said, there isn't no concern. The most plausible endocrine/reproductive risks are around older benzophenone filters, especially oxybenzone/BP-3 and its metabolites, and around homosalate at higher exposure levels. Human studies are mixed and mostly observational, but the biologic plausibility is real enough that European regulators have tightened some limits and the FDA still wants more data. A systematic review of the human evidence on oxybenzone and octinoxate found insufficient evidence to establish causal harm across the endocrine and reproductive endpoints people worry about. So my stance is: absorption is proven, plausible concern exists, clinical harm at current use levels is not established.

Meanwhile, the mineral filters, zinc oxide and titanium dioxide, sit on firmer regulatory ground. The FDA's 2021 proposed order considers both GRASE up to 25%, including nanoscale forms, because they essentially don't penetrate intact skin. The real mineral-filter caution is inhalation, which matters if you use sprays and powders.

My hierarchy of concern, as someone who has worn these products daily for decades:

If ingredient uncertainty genuinely bothers you, you don't need to go into a toxicology rabbithole. Zinc oxide exists. Use it and move on, especially for pregnancy, young kids, very high daily body use, or if the whole topic makes you less likely to wear sunscreen at all.

If you want the ingredient-by-ingredient version, I put the deeper study-linked guide here: How to Choose Sunscreen That Actually Protects You.

Last month (June 2026), the FDA added bemotrizinol to the sunscreen monograph, the first new active sunscreen ingredient permitted in the U.S. since the late 1990s. The order allows it at up to 6%, and it matters for exactly the reasons we care about: bemotrizinol is a photostable filter with strong protection across both UVA and UVB, and it shows low skin absorption, sidestepping the systemic-absorption question that hangs over the older organic filters.

Europe and many other markets have had this molecule (as Tinosorb S) for years, which is why sunscreen nerds have been bringing home European formulas in their luggage. The elegant, cosmetically pleasant UVA protection Americans have envied is finally coming to U.S. shelves. Expect reformulated products over the next year or two; they'll be worth watching for the UVA gap alone.

The most common pushback I get: "Doesn't sunscreen tank your vitamin D?"

In tightly controlled artificial-UV experiments, sunscreen can suppress vitamin D synthesis. In actual humans living actual lives, field studies show real-world sunscreen use has little effect on vitamin D status, largely because nobody applies it perfectly or everywhere. A field trial on a high-UV Tenerife holiday found that even optimal sunscreen use allowed vitamin D synthesis while preventing sunburn, and an expert consensus concluded that broad-spectrum sunscreen use is unlikely to compromise vitamin D status in healthy people.

My clinical translation: skin damage is not a vitamin D protocol. If you're worried about your level, measure it, and supplement if it's low. Do not outsource your endocrine system to a sunburn.

Lab studies have implicated oxybenzone in coral toxicity, and UV filters have been detected in waterways and aquatic organisms. Real-world exposure levels and coral science are genuinely contested, and climate change is the far bigger reef threat. Plus, "reef safe" on a label is marketing, not a regulated standard. If you want to be extra careful around reefs: cover most of your body with UPF clothing, use mineral filters on what's left, respect local bans (Hawaii and others prohibit oxybenzone/octinoxate), and skip the debate entirely.

Match the product to the job. There is no single best sunscreen; there's a best sunscreen for a use case.

One rule that outranks the whole list: A mediocre product used correctly outperforms a perfect product applied once at 8 a.m.

I hope this issue gives you the right sunscreen tool to survive one of the hottest weeks in history. It's still one of the few interventions where a randomized trial, a mirror, and a dermatologist all agree. Wear it like you mean it: enough of it, every day.

Hillary Lin, MD

I'm due for a video on sunscreen! But if you want to watch my content on skin aging, here's a good video:

Watch on YouTube | Subscribe to The Longevity Show

💉 GLP-1s are done staying in the weight-loss lane. In the Lancet REIMAGINE 3 trial, CagriSema added to basal insulin cut HbA1c by 2.1 to 2.3 points and body weight by 10 to 12% in hard-to-control type 2 diabetes.

🧠 Alzheimer blood tests are arriving with a very important asterisk. A JAMA Neurology evaluation of Lumipulse p-tau217/Aβ42 flagged 30 of 75 amyloid-negative people as positive or indeterminate, so the while it's exciting we have a test, there seem to be a high rate of false negatives.

🫀 Finally, an AI use case that is not pretending to be your doctor. A Nature ECG model spotted a hidden sudden-death signal in ordinary tracings, finding a 2.2% group with 7.0% annual risk that usual testing would have missed.

🩺 The blood-pressure win is not a far-off retirement prize. A Nature Medicine meta-analysis of 51 randomized trials found a 5-mmHg systolic drop lowered major cardiovascular events within year one, which is a nice reminder that normalizing BP can work faster than people think.

♀️ For women’s brain aging, the scale is not the whole plot. In Diabetologia, higher waist-to-hip ratio, visceral fat, and liver fat tracked with lower hippocampal insulin responsiveness with age, especially after menopause.

😴 Sleep tech is trying to disappear. BCGNet, trained on 595,946 hours, staged sleep and estimated apnea burden from an under-pillow sensor.

🧪 Peptides are entering their paperwork era. The FDA compounding committee will weigh BPC-157, KPV, TB-500, MOTs-C, DSIP, Semax, and Epitalon for 503A eligibility, and BMJ is already questioning who gets to sit in judgment.

DESA Conference, July 10–11, New York. Inaugural dry eye and ocular-surface conference: niche, clinical, and exactly the sort of thing that becomes more important once you notice it.

Science of Skin Summit, September 17–20, Austin, TX. I’ll be speaking on AI in dermatology and skin/hair as windows into biological age.

MVMNT Longevity Summit, September 22–23, Coronado, CA. Evidence-based longevity medicine, performance health, and clinical innovation. My role is being finalized.

Livelong Women’s Health Summit NYC, September 25–26, New York. Women’s health and longevity; summer pricing runs through July 10. My role is still being finalized.

Science of Skin Longevity Summit, February 19–21, 2027, Scottsdale, AZ. Planning to join faculty for a practical skin-longevity talk on biological age, AI/photo analysis, and what patients see in the mirror.

No sunscreen affiliate in this issue because the point is not to sell you SPF.

A few reader-supported partners that fit the broader longevity stack:

If you want physician-guided biological age testing, start on the testing page. It includes epigenetic age testing with consultation, plus organ-specific proteomic and SystemAge assessments when they fit the clinical question.

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