What Is UV400 Protection? A Parent's Guide to the Number on the Label

You're in a shop holding a pair of kids' sunglasses in one hand and your phone in the other, trying to work out whether "UV400" on the tag means anything or whether it's just marketing.

It's one of the few numbers on sunglasses that means something specific. It's also the one worth checking.

What does UV400 protection mean?

UV400 means the lenses block ultraviolet light up to a wavelength of 400 nanometres.

The number matters because of where it sits. Ultraviolet light that reaches us comes in two bands worth knowing about: UVB, at 280 to 315 nm, and UVA, at 315 to 400 nm. A lens rated UV400 covers both, right to the top of the UVA range. Above 400 nm there's no UV at all, that's where visible light starts.

So UV400 isn't a ceiling someone picked for the marketing. It's the whole band.

Is UV400 the same as 100% UV protection?

Yes. They're two ways of describing one thing.

"Blocks 100% of UVA and UVB" is the benefit. "UV400" is the spec that delivers it. A lens blocking up to 400 nm blocks 100% of the UVA and UVB reaching it, because there's no UV left above that line.

If a label gives you one and not the other, it's the same claim in different words. If it gives you neither, just "UV protection," or a percentage with no wavelength attached, then you don't actually know what you're getting.

Is UV400 protection good enough?

For everyday sun, yes. UV400 is the ceiling, not a mid-tier option. There's no UV500.

What UV400 doesn't tell you is anything else about the pair in your hand. Two lenses can both be UV400 and have nothing else in common: one a tinted plastic disc, the other a proper multi-layer lens. One might shatter where the other flexes. Only one of them might be polarized. And only one of them will still be on a two-year-old's face by lunchtime.

Insist on UV400, then keep asking questions.

UV400 vs polarized: which is better?

This one comes up constantly, and the "or" in it is doing the damage. They aren't competing. They do two unrelated jobs.

UV400 is the protection. Polarization is the comfort, and with kids the comfort does protective work too, because a child who isn't squinting is a child who keeps the sunglasses on. One parent put it this way in a review: "the polarization is real, you can tell the difference immediately."

So you want both. Every pair of Baby Sunnies® has 9-layer UV400 polarized lenses, which takes the choice off the table.

How to check a pair actually has UV400

Four things, roughly in order of how much they tell you.

1. Look for a standard, not an adjective. "CE certified to EN ISO 12312-1" is a testable claim. "UV protection!" on its own isn't.
2. Check for the wavelength. UV400, or "up to 400 nm." A percentage with no number behind it is a percentage of nothing in particular.
3. Ask who tested it. Certifications come from test reports, and brands that have them will tell you.
4. Ignore the tint. Darkness has nothing to do with UV blocking. A pale lens can be UV400 and a very dark one can block almost nothing. This is the most common mix-up going, and it's why "these look dark enough" isn't a check.

What this means for babies and kids

Little eyes are extra sensitive to UV rays, and kids spend more of the day outside than we do. That's worth knowing rather than worrying about, and it changes one thing: make the pair they actually wear a real pair.

For 0–24 months, the strap does the work. Little heads don't hold arms well, and a soft adjustable strap turns sunglasses into something that stays put. From 3–8 years the frames get more active lives, so flexible silicone that bends instead of snapping, plus shatter-resistant lenses, matter more than they sound like they should. At both ages, whatever they wear has to survive being sat on. "Virtually unbreakable" isn't a slogan here. It's the difference between one pair a summer and one pair a week.

Shop by age: Baby Sunglasses (0–24 months) or Kids Sunglasses (3–8 years). You can also browse Boys and Girls.

Quick answers

Do kids need polarized sunglasses?
Not strictly. UV400 is the part that protects. But polarization is what stops the squinting, and a pair that's comfortable is a pair that stays on, so it does real work.

Should kids wear sunglasses at all?
Outdoors on bright days, yes, same as adults. Sun protection eyewear is ordinary kit rather than a precaution. We went into this in more detail in do babies need sunglasses.

How do I get a baby to wear sunglasses?
Start in the shade, keep the first go short, and use a strap. Most of the resistance parents describe turns out to be about fit. Glasses that slide get pulled off. Ones that sit properly get forgotten about. For the newborn end of the range, see how to get a baby to keep sunglasses on.

Does a darker lens mean more protection?
No. Tint and UV blocking are unrelated, so check for UV400.

Product is sun protection eyewear, not a medical device. Consult an eye care professional for vision concerns. Baby Sunnies® sunglasses are CE certified to EN ISO 12312-1 and REACH compliant. Ages 0–24 months (baby) and 3–8 years (kids); adult supervision required.