HeraSphere #45: What the SPF?

Hi friends,

My teenage daughter and I had a standoff at the beach last week. She wanted to apply sunscreen at the last minute before going outside. I said apply it earlier. Neither of us backed down. She did it her way, and I let it go.

UV exposure causes 80 to 90% of visible skin aging. I am someone prone to sunspots and hyperpigmentation. Despite being very careful about sun exposure (sunscreen hats, umbrellas and more…), I realized I didn’t understand much about how to protect my skin.

I spent a few days researching everything SPF and UPF, and here it is to share with you.

The TL;DR

• SPF measures how long before you burn, nothing else. It says nothing about the rays that cause aging and dark spots.

• "Broad spectrum" covers both UV ray types: UVA and UVB. Without it, you're only protected against sunburn.

• The FDA just approved the first new sunscreen ingredient in 25 years. It closes a UVA protection gap that left American sunscreens behind European formulas for decades.

• Clothing protects better than sunscreen, but only the right clothing. A wet cotton t-shirt at the beach offers almost no UV protection.

• Reapplication matters more than the SPF number. An SPF 30 reapplied every two hours outperforms an SPF 100 applied once.

The Two Rays You Need to Know

The sun emits two types of ultraviolet rays. They do completely different things.

• UVB burns. UVA ages. UVB hits the outermost skin layer and causes sunburn. UVA penetrates deeper into the dermis, the structural layer where collagen, elastin, and pigment-producing cells live, and causes dark spots, uneven texture, and premature aging.

• UVA damage is invisible until it isn't. No redness, no burn. It accumulates silently and shows up years later as spots and texture changes that no serum fully reverses.

• UVA drives the majority of hyperpigmentation. It triggers melanin overproduction deep in the skin. Melanin is your skin's defense pigment. More UVA exposure means more spots.

• Visible light makes pigmentation worse too. Blue light from the sun triggers melanin production, especially in women with melasma. Tinted sunscreens with iron oxides block visible light. A plain SPF, even mineral, doesn't.

• Your car's side windows block almost no UVA. Windshields have a protective interlayer. Side and rear windows don't, letting through 60 to 80% of UVA. Dermatologists track consistently higher skin damage on the left side of the face in US drivers. Ceramic window film fixes this.

What SPF Actually Measures

SPF measures how much more UV energy is required to burn protected skin versus unprotected skin. SPF 30 means 30 times more energy is needed to cause redness. That's it. It only measures UVB.

• The scale is not linear. SPF 15 blocks 93% of UVB. SPF 30 blocks 97%. SPF 50 blocks 98%. SPF 100 blocks 99%. The difference between SPF 30 and SPF 100 is two percentage points. So don’t sweat the number.

• SPF says nothing about UVA. A product can have SPF 100 and still leave you poorly protected against the UVA rays causing the most long-term damage.

• Most people apply half the required amount. Lab testing uses a full shot glass for the body and a nickel-sized amount for the face. At half the dose, SPF 50 performs closer to SPF 7.

• Mineral sunscreen works on contact. Chemical needs 20 minutes. Zinc oxide and titanium dioxide physically block rays the moment they touch skin. Chemical filters need time to bind. If you're using mineral, applying at the last minute is fine.

The Hierarchy of Sun Protection

UPF (Ultraviolet Protection Factor) is the clothing equivalent of SPF, with one key difference: UPF covers both UVA and UVB. SPF only covers UVB. UPF 50 blocks 98% of all UV radiation and maintains that rating when wet.

• Most beach clothing offers almost no protection once wet. A dry white cotton t-shirt is UPF 5 to 9. Wet, it drops to UPF 3 to 4.5. Lycra coverups are similar. Conventional swimwear is not sun protection.

• UPF 50 synthetic fabric holds its rating wet or dry. Polyester and nylon maintain protection because it's built into the fiber, not a coating that washes away. This is the only clothing worth counting on at the beach.

• Straw hats are not sun protection. A wide brim helps, but loosely woven straw has a UPF as low as 5 to 10. Light coming through the crown means UV is coming through. Tightly woven synthetic or canvas rated UPF 50 is the reliable choice.

• A UV umbrella blocks 98 to 99% of UV. A regular umbrella blocks about 75%. UV umbrellas use specialized coatings and tight synthetic weave to achieve UPF 50+. A regular umbrella provides shade but not UV protection. Women across Asia have used UV umbrellas for decades as standard practice, and now I know why.

• Spray sunscreen underperforms, and most chemical sprays harm reefs. Overspray lands on sand, not skin, so most people apply far less than the label suggests. Aerosol cans atomize the product into particles small enough to inhale into the lungs, and only about half the can's weight is actual sunscreen, the rest is propellant. Chemical filters like oxybenzone also wash into water and have been linked to coral bleaching. Mineral lotion, rubbed in by hand, is still the most reliable choice for you and for the reef.

• The beach compounds exposure by up to 50%. UV reflects off sand and water, hitting you from above and below simultaneously.

• The full hierarchy: UPF 50 synthetic clothing. UPF rated wide-brim hat. UV umbrella for stationary time. Broad spectrum mineral SPF 50 on all exposed skin. Reapply every two hours or after swimming.

The Newest Ingredients & Formats Worth Knowing

• Bemotrizinol was FDA-approved June 9, 2026 — the first new US sunscreen filter in 25 years. It's a chemical filter with strong, photostable (meaning it doesn't break down in sunlight) broad-spectrum UVA and UVB coverage. It has been in European and Asian sunscreens since 1999 under the names Tinosorb S and Parsol Shield.

• This is why European sunscreens outperform most US options on UVA. American formulators have been limited to filters approved in the late 1990s. Avobenzone, the main UVA filter in US products, degrades in sunlight while Bemotrizinol doesn't.

• Nano zinc oxide is in most modern mineral sunscreens, and it's likely fine. Manufacturers shrink zinc oxide particles to eliminate white cast. Human studies show nano zinc oxide doesn't penetrate past the skin's outer layer. The unresolved question is narrower than people assume: it's about spray/inhaled forms, not the lotion on your face. Non-nano formulas exist if you want to remove the variable entirely; look for "non-nano" on the label.

What I'm Using and What I'm Changing

The research changed how I think about my own routine. Here's where I landed.

• Face: Anthelios Ultra-Light Fluid sourced from Europe, EltaMD UV Clear as backup. European Anthelios contains Mexoryl 400 and Tinosorb S, filters unavailable in the US version. It provides stronger UVA coverage than anything currently on US shelves. EltaMD UV Clear (SPF 46, zinc oxide, niacinamide) is what I use when it runs out.

• Body: Think Sport or Think Baby. Both Think formulas use 20% zinc oxide for genuine broad-spectrum coverage. My husband prefers Badger Mineral since it goes on smoothly without a white cast. It has is a clean, shorter-ingredient option, but my youngest daughter objects to the slightly chemical non-scent scent.

• Straw hats are out. I wore one religiously and kept getting sunspots on my face. Now I know why. Switching to this wide-brimmed UPF 50 hat immediately.

• My ultracompact UV umbrella is in, especially for Asia this summer. We are traveling to China and Japan this summer. I got a small one that folds up to the size of a phone for sightseeing trips under the blazing sun. I think of the inconvenience as protecting my investment in my skin.

• Ceramic film for my car windows is scheduled. My left cheek has been absorbing UVA through the side window every day. I’m finding a shop to take out that unneeded UV factor.

What This Changed

I thought I had sun protection figured out. The UPF clothing, the European sunscreen, the religious hat wearing. Turns out I had the right instincts and the wrong execution on several of them. Wet cotton is not coverage. Straw is not a sun hat. A regular umbrella is not meaningful UV protection.

The through-line: things that look like protection and aren't are more dangerous than nothing, because they create false confidence. Now I know exactly what each layer in my routine is actually doing or not.

My girls are really good about applying sunscreen, but the negotiation with my teenage sun continues. If anyone has solved that one, please send me a note!

In broadspectrum we trust,

Lilly

P.S. If you have a friend who invests in her skin and but hasn’t deep dived on SPF, forward this her way. She may be spending her dollars in the wrong place.

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Note: While I love diving deep into research and sharing what I've learned about women's health and wellness, I want to be crystal clear: I'm a passionate health advocate and researcher, not a medical professional. Think of me as your well-informed friend who does extensive homework – but not your doctor.

Everything I share in HeraSphere comes from careful research and personal experience, but it's meant to inform and inspire, not to diagnose or treat any medical conditions. Your body is uniquely yours, and what works for one person might not work for another. Always consult your healthcare provider before making significant changes to your diet, exercise routine, or wellness practices, especially if you have underlying health conditions or take medications.

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