That SPF Number Isn't Telling You What You Think It Is

Summer hits and suddenly sunscreen is everywhere. On the shelf, in your group chat, all over your feed. And the more you read, the more confusing it gets. Is a higher SPF worth it or not? Mineral or chemical? Is the stuff you've used for years secretly bad now? And then someone pops up online telling you to skip sunscreen entirely and just eat more red fruit.

It's a lot of noise for something that should be pretty simple.

A lot of what gets passed around about sunscreen is half right, which is exactly what makes it stick. So I want to walk through the things parents hear most, what's actually true, what isn't, and the few things that really do keep your kid protected.

Can you eat your way to sun protection?

Every summer a version of this goes viral, and this year it's watermelon juice, the idea that eating the right foods turns your skin into its own sunscreen.

There's a kernel of truth here, which is part of why it spreads so easily. Watermelon, tomatoes, and red peppers all contain lycopene, an antioxidant, and a diet rich in it may slightly reduce how much your skin reddens after time in the sun. But slightly really is the whole story, because that small assist is nowhere near enough to protect a kid who's outside playing for hours.

So please, eat the watermelon and load up on red fruits and veggies all summer, because they're genuinely good for your kids. Just know that's a snack, not skin protection, so the sunscreen still needs to go on too.

What SPF actually measures

Here's the big one, the thing almost everyone gets wrong. SPF does not tell you how long you can stay outside. A lot of us grew up believing that a higher number meant more hours of coverage, like SPF 50 buys you twice the time of SPF 25. That's not how it works.

What SPF actually measures is how well a sunscreen filters UVB rays, the ones that burn your skin, before your skin starts to redden. And when you look at the real numbers, the difference between the high SPFs is smaller than the marketing makes it feel:

• SPF 15 filters about 93% of UVB rays

• SPF 30 filters about 97%

• SPF 50 filters about 98%

So going from SPF 30 to SPF 50 isn't doubling anything, it's just a couple of percentage points. No sunscreen blocks 100%, and a higher number on the bottle doesn't mean you can put it on once and forget it for the day.

If there's one thing I want you to remember, it's that SPF 30 is a solid floor for kids, SPF 50 is great if that's what you've got, and the number was never the thing that lets you skip reapplying or staying in the shade during peak hours. It's one layer of protection, not a force field.

UVA, UVB, and why "broad spectrum" matters

If SPF only speaks to UVB, you might be wondering what's handling the rest, and that's where broad spectrum comes in.

There are two kinds of UV rays that reach your skin. UVB is the one that burns, so an easy way to keep it straight is B for burn. UVA goes deeper and is tied more to skin aging and longer-term damage, so think A for aging.

Here's the part that surprises a lot of people: UVA can pass right through glass, which means your kid can be getting some UVA exposure sitting by a sunny window or riding in the car, even on a day when nobody's outside long enough to burn. It's quietly there in a way UVB isn't.

That's the whole reason "broad spectrum" is worth looking for on the label. A sunscreen that only lists an SPF number is really just speaking to the UVB side, the burning rays. Broad spectrum means it covers both UVA and UVB, so you're getting the fuller protection, not just the part you can feel. It's the phrase to scan for when you're standing in the aisle trying to pick something.

Mineral or chemical: which is better for my kid?

This is probably the question I get most, and there's a lot of worry packed into it, so let me take some of the pressure off right away. Both mineral and chemical sunscreens are widely used and regulated, and major pediatric and dermatology groups consider them reasonable options for protecting your kid's skin.

The quick version of how they differ: mineral sunscreens, the ones with zinc oxide or titanium dioxide, mostly sit on top of the skin and act as a physical block. Chemical sunscreens absorb into the skin and work by absorbing UV rays. A lot of parents lean mineral for babies and younger kids, or for sensitive or eczema-prone skin, because it tends to be gentler and less irritating.

You've probably also seen a lot of fear online about specific ingredients, oxybenzone being the big one. Here's the honest context: oxybenzone is a long-used, FDA-regulated ingredient, and any sunscreen is far better than skipping it. That said, the American Academy of Pediatrics does suggest avoiding oxybenzone when you can, citing concerns about mild hormonal effects. The takeaway isn't that you need to throw out a product you already own. It's more that if you're choosing something new, picking one without oxybenzone is a reasonable call. Plenty of brands have already moved away from it, so it's easier to avoid than it used to be.

If I'm being honest, the most important factor isn't mineral versus chemical at all. It's whether you'll actually use the sunscreen and reapply it the way you're supposed to. The best sunscreen for your family is the one you'll reliably put on.

I went deep on all of this, ingredients, formulation, why zinc oxide is a bit of a workhorse, with a sunscreen formulation expert on the PedsDocTalk podcast, so if you want to understand what's actually in the bottle, that conversation is a good listen.

The part that actually determines protection

Here's the thing that matters more than which bottle you picked: how you use it. A great sunscreen applied once in the morning and never again is not doing the job you think it is by mid-afternoon.

A few tips worth keeping in mind:

• Reapply every two hours, and sooner if your kid has been swimming, sweating, or toweling off. Water-resistant formulas help, but nothing is truly waterproof, so the towel-dry moment is a built-in reminder to put more on.

• Pack the bottle if you're out for the day. The reapplying matters as much as that first application at home.

• Don't skip the easy-to-miss spots: the ears, the nose, the back of the neck, the hairline and the part in the hair, the tops of the feet, and the backs of the knees.

One trick I love for the awkward spots and squirmy faces is keeping a dedicated makeup brush in the sunscreen bag. A soft brush makes it much easier to get the scalp, around the ears, and the bridge of the nose without a fight, and somehow it bothers them less than fingers do.

And a quick word on spray sunscreens, since they're so much easier with a moving toddler. They're fine to use, with a couple of small things to keep in mind:

• Spray it into your hands and rub it in rather than misting it at your child's face.

• Apply it outdoors or somewhere ventilated so they're not breathing it in.

• Make sure you're actually rubbing it in, so you get even, full coverage.

A quick note on babies

Things look a little different for the youngest ones. For babies under 6 months, I'd rather keep them out of direct sun when you can, leaning on shade, a stroller canopy, a hat, and lightweight clothing that covers their arms and legs.

One thing worth flagging here: use the stroller's built-in canopy rather than draping a blanket or muslin over the top. It seems like a quick shade fix, but covering the stroller can trap heat and cut off airflow, which can let things get dangerously warm inside without you seeing it. Open shade and the canopy are the safer way to go.

If you're somewhere with no good shade and some sun is unavoidable, a small amount of mineral sunscreen on the spots you can't cover, like the face and the backs of the hands, is okay.

Once they're over 6 months, you can use sunscreen more freely on exposed skin, with the same broad-spectrum, reapply-often approach as everyone else. Shade and clothing still do a lot of the work, sunscreen just joins in as another layer.

Dr. Mona, does sunscreen mean my child will be vitamin D-deficient

Good news: sunscreen is not the reason your kid's vitamin D is low. Even with daily use, no one applies it perfectly enough to block every ray, and kids are getting sun in between applications too. If you're genuinely worried about vitamin D levels, that's a conversation worth having with your pediatrician, but skipping sunscreen is not the fix.

The sunscreens I reach for

When I'm choosing a sunscreen for my own kid or recommending one to families, I'm looking for a few simple things: broad-spectrum coverage, SPF 30 to 50, water-resistant, and a mineral formula with zinc oxide, which tends to be the gentlest option for little ones and sensitive skin. With any new product, it's smart to do a small patch test first to make sure their skin agrees with it.

Here are the ones I come back to:

• Coppertone Pure and Simple Baby: a gentle, fragrance-free mineral option that holds up well on sensitive skin.

• Thinkbaby SPF 50+: a mineral formula that rubs in more easily than you'd expect for zinc, which helps with squirmy application.

• Aveeno Baby Continuous Protection SPF 50: carries the National Eczema Association seal, so it's a nice pick for eczema-prone skin.

• Neutrogena Pure and Free Baby Mineral SPF 50: another eczema-friendly mineral option that's easy to find at most stores.

• Blue Lizard SPF 50: a longtime family favorite that works well for everyone, not just the babies.

I personally don’t mind mineral sunscreen. It does leave a white cast but it reminds me of summer and to reapply. A visual cue of fun and reapplication in one. 

Sunscreen I use (I’m a Florida girly who’s out in the sun often):

• Daily on the face: Supergoop! Glowscreen SPF 40 - Glowy Primer + Broad Spectrum Tinted Sunscreen - Helps Filter Blue Light - Hydration - Hyaluronic Acid & Vitamin B6

• Another option for daily face use: La Roche-Posay Anthelios Sunscreen SPF 40, Ultra-Light Fluid Broad Spectrum SPF 40, Face Sunscreen with Titanium Dioxide Mineral, Lightweight & Fast-Absorbing, Oil-Free, Matte Finish

• Coppertone Sport Sunscreen SPF 50

Please note: Some of the links above are affiliate links. This means that if you make a purchase through one of them, I may receive a small commission at no additional cost to you. Using these links is one small way to support PedsDocTalk, and I truly appreciate it.

The bottom line

Sun safety really comes down to a few simple habits, even if the internet makes it feel complicated. Pick a broad-spectrum sunscreen that's SPF 30 or higher, put it on and reapply it, and pair it with shade, hats, and clothing when you can. The exact brand matters far less than actually using it.

And try not to let the noise pull you toward all-or-nothing thinking, whether that's fear of the sun or fear of sunscreen itself. Kids are meant to be outside having the long, messy, sweaty summer days that are so good for them. A few small habits let them do exactly that, with their skin protected while they're at it.

Ask Dr. Mona

An opportunity for YOU to ask Dr. Mona your parenting questions!

Dr. Mona will answer these questions in a future Sunday Morning Q&A email. Chances are if you have a parenting concern or question, another parent can relate. So let's figure this out together!