The Best Sunscreens for Mature Skin in 2026: 10 Derm-Vetted Picks That Won’t Settle Into Fine Lines (or Your Budget)

Skin after 40 doesn’t ask for much. It just wants a sunscreen that hydrates without turning your face into an oil slick, sits under makeup without pilling, and doesn’t highlight every fine line like a museum spotlight. That’s not a tall order. It’s a very specific one, and most sunscreens on the shelf were not formulated with it in mind.

The US sunscreen market is finally catching up. Mineral formulas have been reformulated to skip the chalky ghost cast. Tinted SPFs now double as light coverage instead of a separate foundation step. Korean exports have forced Western brands to compete on texture, not just SPF numbers. And dermatologists have gotten louder about one uncomfortable fact: UV exposure is responsible for the majority of visible skin aging, not the calendar.

We spent weeks cross-referencing dermatologist recommendations, retailer pricing, return policies, and real user feedback from women over 40 to build a ranked list that holds up to scrutiny. No affiliate-driven “top 50” padding. No vague promises. Just ten sunscreens worth the shelf space, sorted by what actually matters when your skin has stopped bouncing back overnight.

Why Sunscreen Is Non-Negotiable After 40 (And What Actually Changes)

Dermatologists have a line they repeat until patients listen: sunscreen is the single most effective anti-aging product in the arsenal. Aderonke Obayomi, MD, a board-certified dermatologist at Mount Sinai in New York, puts it plainly: visible facial aging, fine lines, wrinkles, age spots, and loss of firmness are largely caused by sun exposure, not simply the passage of time. That distinction matters. It means the damage is cumulative and largely preventable, not a fixed script written into your birthday.

What changes after 40 is not the need for protection but the margin for error. Skin loses moisture and collagen, which makes dryness, fine lines, and textural unevenness more visible. A sunscreen that felt fine at 28 can suddenly feel tight, drying, or heavy at 48. Formulas that once disappeared into the skin now settle into creases. The finish matters as much as the filter.

The other shift is pigmentation. Years of UV exposure surface as dark spots, melasma, and uneven tone, and those concerns tend to accelerate around menopause. A broad-spectrum SPF with iron oxides — the pigments that give tinted sunscreens their color — does more than block UV. It also helps shield against visible light, which is a known trigger for stubborn pigmentation. That’s one reason tinted formulas have moved from “nice extra” to “derm recommendation” for many women over 45.

The practical upshot: the best sunscreen for mature skin is not the one with the highest SPF on the shelf. It’s the one you’ll apply every morning without resentment, because consistency beats theoretical protection every single time. “The best sunscreen is the one you’ll actually wear every day,” Dr. Obayomi says. “Texture, finish, and personal preference matter enormously”.

Quick Picks: The Best Sunscreens for Mature Skin in 2026

If you’re not here for the full breakdown, this is the short version. These five cover the most common needs: overall performance, drugstore accessibility, mineral-only formulas, Korean texture, and tinted coverage.

Prices are approximate and move with retailer promotions and shade availability. Check the current listing before you commit.

The Full Ranking: 10 Best Sunscreens for Mature Skin, Tested and Vetted

The ranking below weighs five factors: derm consensus, texture on mature skin, finish under makeup, ingredient profile (hydration, antioxidants, barrier support), and real-world cost per ounce. A $90 sunscreen can earn its price if it replaces both moisturizer and primer. A $15 Korean formula can beat a $50 Western cream if the texture means you’ll actually reapply. Value is not the same as price.

1. EltaMD UV Restore SPF 40 — Best Overall for Mature Skin

EltaMD has become the default dermatologist recommendation for a reason: the formulas are boring in the best way. UV Restore is a zinc oxide–based mineral sunscreen built specifically for sun-damaged and mature skin, and it keeps showing up on derm lists without the usual affiliate noise. The texture is moisturizing without being greasy, and the finish is forgiving on dry patches and fine lines. It layers cleanly over vitamin C and retinol, which is more than most mineral formulas can claim.

The trade-off is tint and cast. UV Restore is not invisible on every skin tone, and it is not the lightest formula on this list. If you have deep skin or prefer a weightless finish, the Korean options below will likely serve you better. But for fair to medium skin dealing with sun damage, redness, or post-procedure sensitivity, this is the safest bet in the category. It is also the sunscreen most likely to be recommended by a dermatologist who has no financial stake in the sale.

At roughly $49 for 1.7 ounces, it is not cheap, but it is not La Mer territory either. One bottle used at the correct dose — about a quarter teaspoon for the face — lasts six to eight weeks with daily morning application. That puts the real cost at roughly $6 to $8 per week, which is less than most people spend on coffee they don’t finish.

2. La Roche-Posay Anthelios Light Fluid SPF 50 — Best Drugstore Pick

The Anthelios line has a cult following for one reason: it makes high-protection sunscreen feel like nothing. The Light Fluid SPF 50 is exactly what the name suggests — a thin, fluid texture that absorbs fast and leaves a satin finish that works equally well on bare skin and under foundation. It has been cited as a drugstore standard by derms and editors across multiple 2026 roundups.

For mature skin, the appeal is the finish. It does not sit on top of the skin or exaggerate texture. It also plays well with moisturizers and serums, which matters if your morning routine involves more than one product. The formula is chemical rather than mineral, so anyone with a strict mineral-only preference should look at the Colorescience or CeraVe picks below. But for the vast majority of users who just want a reliable daily SPF that does not feel like a mask, this is the one to beat at the drugstore price point.

Availability is the other advantage. La Roche-Posay is stocked at Ulta, Target, CVS, Walgreens, and Amazon, which means you can restock on a Tuesday night without waiting for a specialty shipment. That accessibility matters for consistency. A sunscreen you can buy locally is a sunscreen you will not run out of mid-week.

3. Colorescience Total Protection Face Shield Classic SPF 50 — Best Mineral

Mineral sunscreen has a reputation problem: white cast, thick texture, and the feeling of wearing a clay mask in July. Colorescience Face Shield Classic solves most of that. It is a liquid mineral SPF 50 with a subtle neutral tint that blends sheer on most skin tones, and it contains iron oxide pigments and antioxidants alongside the zinc oxide. Dermatologists recommend it specifically for mature skin dealing with pigmentation, because the tint does double duty: it evens tone and helps block visible light.

The finish is lightweight and slightly mattifying, which is a relief for anyone who has avoided mineral formulas because they felt heavy. It also works as a makeup primer, which means one less step in the morning. The price sits in the mid-to-premium range — around $45 to $55 depending on the retailer — but a little goes a long way, and the pump bottle dispenses a controlled amount instead of flooding your palm.

The caveat is shade range. The “Classic” tint is designed to blend universally, but universal is a marketing word, not a guarantee. If you have very deep skin, test a sample or buy from a retailer with a generous return policy. The formula is excellent; the shade match is the variable.

4. Beauty of Joseon Relief Sun SPF50+ PA++++ — Best Korean Formula

The Korean sunscreen wave is not hype. It is a texture revolution. Beauty of Joseon Relief Sun has become the most consistently recommended Korean SPF for mature skin because it feels like a hydrating serum, not a sunscreen. Rice extract provides antioxidant support and gentle brightening, fermented probiotic extract supports the barrier, and the finish is a soft satin that does not pill under makeup.

For mature skin, the appeal is the lack of compromise. You get SPF50+ and PA++++ — the highest standard UVA rating used in Asia — without the dryness, white cast, or heavy occlusion that make Western high-SPF formulas a chore. It is alcohol-free, which matters for a barrier that is already thinning with age. And the price is almost absurd: typically $15 to $20 for 50 milliliters, which is roughly double the volume of many Western facial sunscreens at a third of the price.

The trade-off is availability and regulation. Korean formulas are sold through specialty retailers like Stylevana, YesStyle, and Jolse, and shipping times can stretch from a few days to a few weeks depending on the warehouse. The US FDA has not approved some of the newer Korean UV filters, which means the formulas sold in the US market may differ slightly from the Korean domestic versions. That is not a safety issue, but it is a transparency issue worth knowing before you assume you are getting an identical product.

5. EltaMD UV AOX Elements Tinted SPF 50 — Best Tinted for Mature Skin

If you want sun protection and light coverage in one step, this is the formula to beat. UV AOX Elements is a mineral tinted SPF 50 that has earned a devoted following among women in their 50s and 60s for its matte, natural finish and its ability to blur pigmentation without looking like foundation. One reviewer in her mid-50s described it as the only complexion product she wears on most days, because it evens out sunspots enough that foundation becomes optional.

The formula contains antioxidants, which is a meaningful addition for mature skin dealing with environmental stress. The tint is sheer but buildable, and it does not settle into fine lines the way heavier tinted moisturizers can. It also wears well under powder or blush, which makes it a practical base for a full makeup day or a five-minute morning routine.

At around $46, it sits in the same price band as UV Restore, and the choice between them comes down to coverage preference. UV Restore is the better option for very dry or reactive skin that needs maximum hydration and zero tint. UV AOX Elements is the better option for anyone who wants a bit of color correction and a more polished finish without a separate foundation step.

6. ISDIN Eryfotona Ageless SPF 50 — Best for Sun-Damage Repair

ISDIN occupies a niche that few sunscreens address directly: repair. Eryfotona Ageless contains DNA Repairsomes, an enzyme complex that the brand claims helps repair existing sun damage at the cellular level, alongside broad-spectrum UV protection. Dermatologists who recommend it tend to position it for patients with a history of skin cancer or significant cumulative sun exposure, not just everyday prevention.

That positioning explains the price — around $50 for a relatively small bottle — and the texture, which is lightweight and silky rather than rich. It is not the most moisturizing option on this list, so very dry skin may need a hydrating serum underneath. But for someone who has spent decades in the sun and wants a formula that treats protection and repair as a single step, it is one of the few products with a credible claim in that space.

The tint is sheer and the finish is natural, which makes it wearable on bare skin. It is not a replacement for dermatologic care if you have a history of skin cancer, but it is a sensible daily companion to that care.

7. CeraVe Hydrating Mineral SPF 50 — Best Budget Mineral

CeraVe has built its reputation on ceramides and no-nonsense formulations, and the Hydrating Mineral SPF 50 is the budget-friendly entry point for anyone who wants a mineral formula without paying dermatologist-brand prices. At around $17 for 2.5 ounces, it is the cheapest per-ounce option on this list by a wide margin. It contains ceramides and hyaluronic acid, which support the barrier and help offset the drying tendency of some mineral filters.

The trade-off is texture. This is a thicker cream, and it can leave a visible cast on deeper skin tones or when applied too generously. It also takes a minute or two to settle, which is not ideal if you are rushing out the door. But for dry, sensitive, or rosacea-prone skin that wants a no-frills mineral SPF at a price that makes daily reapplication feel reasonable, it is hard to argue with the value.

One practical note: the pump bottle is generous, and the formula is stable enough to keep in a bathroom cabinet for the standard 12 months after opening. That makes it a good option for body application as well, especially for arms and hands, which are often the first places to show sun damage.

8. Supergoop! Unseen Sunscreen SPF 50 — Best Under Makeup

Supergoop! built its brand on the “invisible” sunscreen premise, and Unseen Sunscreen SPF 50 is the formula that made the category mainstream. It has a velvety, primer-like texture that fills in texture without feeling silicone-heavy, and it creates a smooth base for foundation without pilling or flaking. For mature skin, the appeal is the blur effect: it softens the look of pores and fine lines without adding another layer of product.

The formula is chemical rather than mineral, and it contains silicones, which some users with sensitive skin prefer to avoid. But for anyone whose primary frustration is sunscreen ruining their makeup, this is the most reliable fix on the market. It is also widely available at Sephora, Ulta, and Amazon, which means returns and exchanges are straightforward if the texture does not agree with your skin.

At around $38, it is priced in the mid-range. It is not the best value per ounce, but it earns its keep if it replaces a separate primer. That is the calculation that matters: a $38 sunscreen-primer hybrid is cheaper than a $28 primer plus a $30 sunscreen that you never wear because it pills.

9. La Mer The Broad Spectrum Face Sunscreen SPF 50 — Best Splurge

La Mer’s sunscreen is expensive. There is no way around that. At roughly $100 for 1.7 ounces, it costs more than some people spend on a week of groceries. But the formula is genuinely lovely: a rich, cushiony texture that feels more like a luxury moisturizer than a sunscreen, with a silky finish that encourages daily use. Dermatologists who recommend it tend to mention the experience as much as the protection — the texture is the point.

For very dry mature skin, that richness is a feature, not a bug. It layers comfortably over serums and creams, and it does not leave the tight, drawn feeling that lighter chemical formulas can cause in low humidity. The SPF 50 rating is solid, and the finish is elegant under makeup. It is not a rational purchase in the way a $17 CeraVe is rational. It is a purchase you make if the ritual of skincare is part of what keeps you consistent.

“Consistent” is the key word. A $100 sunscreen that you look forward to applying every morning is cheaper in the long run than a $30 sunscreen that sits unused in a drawer because you dread the texture. That is not a defense of luxury pricing. It is a defense of matching the product to the habit.

10. Brush On Block SPF 30 Mineral Powder — Best for Touch-Ups and Scalp

Powder sunscreen is not a replacement for a base layer of lotion or fluid. It is a reapplication tool, and for mature skin it solves two specific problems: touching up over makeup without disturbing it, and protecting the scalp and hairline, which are common sites for sun damage that people forget to cover. Brush On Block is a mineral powder SPF 30 with a built-in brush applicator, and it is one of the few powder formulas that dispensers enough product to actually deliver meaningful protection.

The finish is matte and slightly blurring, which makes it useful for shine control on the T-zone. It is not hydrating, so it will not help dry skin, and it is not a standalone sunscreen for a full day outdoors. But as a mid-day touch-up for the part line, the tops of the ears, and the back of the neck, it fills a gap that liquid formulas cannot.

At around $25 to $30, it is a reasonable add-on rather than a primary purchase. Think of it as insurance for the areas you miss with your morning application.

Tinted vs. Untinted: What Mature Skin Actually Needs

Tinted sunscreen has moved from a cosmetic afterthought to a dermatologic recommendation for a subset of mature skin concerns. The pigments — typically iron oxides — do more than even out tone. They help block visible light, which is a known contributor to melasma and post-inflammatory hyperpigmentation. For anyone dealing with stubborn dark spots that seem to worsen despite diligent SPF use, a tinted formula is often the missing piece.

But tinted is not universally better. If your skin is very dry or reactive, the additional pigments and coverage can feel heavier than an untinted fluid. If you have deep skin, the shade range in tinted sunscreens is still frustratingly narrow, and a “universal” tint often means “universal if you are light to medium.” If you wear full-coverage foundation daily, a tinted sunscreen underneath is redundant and can cause pilling.

The practical rule: choose tinted if you want light coverage, are dealing with pigmentation, or want to skip foundation on low-effort days. Choose untinted if you prefer a weightless feel, have very sensitive skin, or plan to layer a separate complexion product. There is no moral superiority in either direction. The best tinted sunscreen for mature skin is the one that matches your actual morning routine, not the one that photographs best in a review.

Mineral vs. Chemical Filters: The Real Trade-Offs After 50

Mineral sunscreens — zinc oxide and titanium dioxide — sit on top of the skin and physically reflect UV rays. They are naturally broad-spectrum, which means they protect against both UVA and UVB without the formulation guesswork that sometimes accompanies chemical filters. They are also generally better tolerated by sensitive or reactive skin, which is a meaningful advantage after 40, when the barrier is thinner and more prone to irritation.

The downside is texture and cast. Mineral filters are white powders, and unless they are micronized or tinted, they can leave a ghostly film, especially on deeper skin tones. They can also feel drying, which is a problem for mature skin that is already losing moisture. Modern formulations have improved dramatically, but the category still asks you to trade a bit of elegance for a bit of gentleness.

Chemical sunscreens absorb UV rays and convert them into heat. They tend to be lighter, more invisible, and easier to formulate into elegant textures, which is why so many of the best Korean and drugstore fluids are chemical-based. The trade-off is potential irritation for sensitive skin, and the ongoing regulatory question marks around some older filters. In the US, the FDA has not approved several of the newer chemical filters used in Europe and Asia, which means American chemical sunscreens are working with a narrower palette than their international counterparts.

For mature skin, there is no universal winner. If your skin is reactive, rosacea-prone, or post-procedure, mineral is the safer default. If your priority is texture, invisibility, and daily wearability, a well-formulated chemical fluid may serve you better. The best sunscreen for aging skin is the one that matches your skin’s tolerance and your willingness to reapply.

How to Choose a Sunscreen for Mature Skin (The Non-Negotiable Checklist)

What SPF and PA rating actually matter?

SPF measures UVB protection — the rays that cause sunburn and contribute to skin cancer. PA measures UVA protection — the rays that penetrate deeper and drive photoaging, pigmentation, and loss of firmness. For mature skin, both matter. A minimum of SPF 30 is the standard dermatologist recommendation, with SPF 50 offering a meaningful buffer for extended outdoor time. PA++++ is the highest UVA rating used in the Korean and Japanese systems, and it is a useful shorthand for formulas that take UVA seriously.

US labeling does not use PA ratings, but “broad-spectrum” on a US label indicates UVA protection proportionate to the SPF. It is not as precise as PA++++, but it is the best available shorthand in the American market. If a formula lists “broad-spectrum” and SPF 50, it is doing the baseline job. If it also lists PA++++, it is exceeding the US minimum.

Which ingredients help (and which to skip)?

Hydration is the first priority. Hyaluronic acid, glycerin, and ceramides help offset the moisture loss that accelerates after 40. Antioxidants — green tea, niacinamide, vitamins C and E — support the skin’s defense against environmental stress and help calm irritation. Barrier-supporting ingredients like panthenol and centella are useful if your skin is reactive or you use retinoids.

Drying alcohols (denatured alcohol, SD alcohol) are worth avoiding if your skin is dry or sensitive. They are not inherently evil — they improve texture and absorption — but for a barrier that is already compromised, they can tip the balance toward irritation. Fragrance is another common trigger for sensitive mature skin, especially around the eyes and mouth.

Texture, finish, and the “will I actually wear it?” test

This is the least scientific criterion and the most important. A sunscreen that feels heavy, pills under makeup, or stings your eyes will not get used, no matter how good the ingredient list looks. Mature skin tends to do best with fluids, serums, and lightweight lotions rather than thick creams, unless the skin is very dry. Matte finishes can emphasize texture; dewy finishes can look greasy. The sweet spot is usually a satin or natural finish that neither flattens nor shines.

The practical test: apply the sunscreen to your bare face on a normal morning, then go about your routine. If you find yourself wanting to wash it off by noon, it is the wrong formula for you. If you forget you are wearing it, it is the right one.

The Full-Cost Comparison: Price per Ounce, Returns, and Hidden Fees

Sunscreen pricing is deliberately confusing. A $50 bottle that contains 1.7 ounces costs roughly $29 per ounce. A $17 bottle that contains 2.5 ounces costs roughly $7 per ounce. That is a four-fold difference in unit cost, and it does not include the cost of the separate primer or moisturizer that a more expensive formula might replace. The table below standardizes the comparison so you can see the real spread.

The powder sunscreen is the outlier: its per-ounce cost is astronomical because it is a touch-up product, not a primary application. That is not a flaw in the product; it is a flaw in comparing it by unit price. Use the per-ounce metric for lotions and fluids, and judge powders by cost per use instead.

Return policies are another hidden cost. Sephora and Ulta both allow returns on gently used products within 30 days, which is a meaningful safety net for tinted formulas where the shade match is uncertain. Amazon’s policy varies by seller, so check the specific listing before you buy. If you are testing a $50 tinted sunscreen for the first time, buying from a retailer with a generous return policy is worth the few extra dollars you might save elsewhere.

Where to Buy: Retailer Return Policies, FSA/HSA Eligibility, and Shipping

Sunscreen is an eligible expense for Flexible Spending Accounts (FSAs) and Health Savings Accounts (HSAs) in the US, provided it has broad-spectrum protection and an SPF of 15 or higher. That is a meaningful discount if you have pre-tax dollars sitting in either account. The catch is that eligibility is determined by the product’s labeling, not the retailer’s marketing. A tinted moisturizer with SPF 30 may qualify; a foundation with SPF 15 may not, depending on how it is classified. Check the product’s drug facts label before you assume it will clear your FSA card.

Retailer availability varies by brand. EltaMD is sold through dermatologist offices, Dermstore, LovelySkin, and Amazon, but not typically at Sephora or Ulta. La Roche-Posay is everywhere: Ulta, Target, CVS, Walgreens, and Amazon. Colorescience is stocked at Dermstore, Sephora, and the brand’s own site. Korean formulas are concentrated at specialty importers like Stylevana, YesStyle, and Jolse, with shipping times that can range from two days to three weeks depending on the warehouse and the shipping tier you choose.

If you are buying a Korean sunscreen for the first time, order from a retailer with a clear return policy and a US-based customer service channel. The savings are real, but the return logistics are not always as smooth as domestic retail. A $15 sunscreen that costs $8 to return is not a $15 sunscreen.

Buying Sunscreen on a Budget: When “Cheap” Becomes Expensive

The cheapest sunscreen is not the one with the lowest sticker price. It is the one that you use consistently and that does not require a supporting cast of moisturizers and primers to make it wearable. A $17 CeraVe mineral formula that you apply every morning is cheaper than a $49 derm-brand fluid that sits in a drawer because it pills under your foundation. That is the first principle of sunscreen economics, and it is routinely ignored in “best of” lists that rank by ingredient list alone.

The second principle is unit cost versus replacement cost. A $15 Korean sunscreen that replaces both a moisturizer and a primer is a better value than a $15 Western sunscreen that requires a separate hydrating serum underneath. The formula’s texture determines how many other products you need to buy to make it work. That is why the “cheap” option can end up costing more per month than the premium one.

The third principle is return policy as a form of insurance. A generous return window lowers the risk of trying a new formula, which in turn makes it easier to find the one that actually works for your skin. A retailer that accepts gently used returns within 30 days is effectively offering you a trial period. That is worth factoring into the price, especially for tinted formulas where shade matching is a gamble.

There is no prize for buying the most expensive sunscreen. There is also no prize for buying the cheapest. The prize is finding the formula that makes daily application feel effortless, because that is the only variable that reliably predicts whether you will still be wearing it six months from now.

What is the best sunscreen for mature skin under makeup?

Supergoop! Unseen Sunscreen SPF 50 and La Roche-Posay Anthelios Light Fluid SPF 50 are the two most reliable options under foundation. Both have lightweight, primer-like textures that absorb quickly and do not pill. If you prefer mineral filters, Colorescience Face Shield Classic works well as a base because its tint creates a smooth canvas without adding weight.

Is tinted sunscreen better for mature skin than untinted?

Tinted sunscreen is better if you are dealing with pigmentation, because iron oxides help block visible light that can worsen dark spots. It is also better if you want light coverage and want to skip foundation. Untinted is better if your skin is very reactive, if you have deep skin and struggle to find a shade match, or if you prefer a weightless feel and plan to wear a separate complexion product.

What SPF should I use if I’m over 60?

SPF 30 is the minimum dermatologist recommendation for daily use, and SPF 50 offers a meaningful buffer for extended outdoor time. The bigger variable is reapplication: most people apply far less than the tested amount, which means the real-world protection is lower than the label suggests. A well-formulated SPF 30 that you apply generously and reapply is better than an SPF 50 that you apply sparingly and never touch up.

Can I use a Korean sunscreen if I have sensitive mature skin?

Yes, but check the filter list. Korean formulas often use newer chemical filters that are not FDA-approved in the US, and some sensitive skin types react to chemical filters regardless of origin. Beauty of Joseon Relief Sun is alcohol-free and generally well tolerated, but if your skin is reactive, patch-test first or choose a mineral formula like CeraVe or Colorescience. The texture advantage of Korean sunscreens is real; the tolerance is individual.

Are expensive sunscreens actually better for aging skin?

Not inherently. Price buys texture, finish, and formulation elegance, not necessarily better UV protection. A $17 CeraVe mineral sunscreen provides the same baseline broad-spectrum protection as a $100 La Mer formula. The difference is in how they feel, how they layer, and whether you enjoy using them. If the expensive formula is the one you reach for every morning, it is better for your skin in practice. If the cheap one is the one you actually wear, the expensive one is just an expensive bottle on a shelf.

The Bottom Line

The best sunscreen for mature skin is not a single product. It is a match between your skin’s current needs, your morning routine, and your willingness to reapply. EltaMD UV Restore is the safest overall recommendation for sun-damaged or reactive skin. La Roche-Posay Anthelios Light Fluid is the best drugstore option for texture and availability. Beauty of Joseon Relief Sun is the best value if you are comfortable buying Korean formulas. CeraVe Hydrating Mineral is the best budget mineral if you can work with the cast.

Everything else is a trade-off between coverage, finish, hydration, and price. The formula that makes you actually apply SPF every morning is the one that will do the most for your skin over the next decade. That is not a marketing slogan. It is the only variable that reliably predicts whether sunscreen works — and it is the one most “best of” lists conveniently ignore.