The short version
UV rises 10-12% per 1,000m and snow reflects 80%. But most trekkers wear category 3 and are fine. When category 4 is actually worth it.
Snow blindness is sunburn. Not a metaphor — the same injury, on the surface of your eye. And the cruel part is the delay: the damage is done on the pass and the pain arrives six to twelve hours later, usually in a teahouse after dark, when you are hours from anywhere and there is nothing to do but lie in the dark and wait it out.
Almost every other expensive thing on a Nepal packing list can be rented in Thamel for a dollar or two a day. We tell people to do exactly that, and we earn nothing when they do. Eye protection is the one that does not work that way: nobody rents sunglasses, a borrowed pair never seals properly against your face, and this is the item where getting it wrong is an injury rather than an inconvenience.
The short version. A good category 3 wraparound is enough for the great majority of teahouse trekking here — including Everest Base Camp and Gokyo. That is what most trekkers actually wear, and what they report back afterwards. Category 4 earns its place if you will be on snow for hours, crossing a glaciated pass, or you already know you are glare-sensitive. Buy before you fly either way: you cannot rent this, and the Thamel copies are not what they claim.
Why altitude changes the maths
Two things stack up on you, and neither is obvious from the valley.
First, there is simply less atmosphere overhead to absorb ultraviolet. UV intensity rises roughly 10 to 12 per cent for every 1,000 metres you climb. By Kala Patthar at 5,545 m you are dealing with something close to double the ultraviolet you would get at sea level.
Second — and this is the one that catches people — fresh snow reflects up to 80 per cent of the UV that hits it. Dry sand manages about 15 per cent. So above the snowline you are lit twice: once from the sky, once from the ground. That is why glasses that merely sit on your nose are not enough up there, and why the injury so often happens on an overcast day, when nobody thinks to put them on.
Indicative, compounded from the published 10–12% per 1,000 m figure. Real UV on a given morning also depends on season, cloud, ozone and the angle of the sun — treat it as the shape of the problem, not a forecast.
Read the category number, ignore everything else
Under the European standard EN ISO 12312-1, every pair of sunglasses carries a filter category from 0 to 4. It tells you how much visible light gets through — the VLT figure. It is the only number on the box worth your attention, and it is usually printed inside the arm.
| Category | Light through (VLT) | What it is actually for |
|---|---|---|
| 0 | 80–100% | Clear. Safety or fashion. No glare control at all. |
| 1 | 43–80% | Light tint. Overcast days at home. |
| 2 | 18–43% | Medium. An ordinary sunny afternoon. |
| 3 | 8–18% | Most proper sunglasses. Fine for Nepal below about 4,000 m. |
| 4 | 3–8% | Glacier and high altitude. Not legal for driving in many countries — genuinely that dark. |
The trap: “100% UV protection” and “UV400” describe the invisible ultraviolet, not the visible brightness. A dark-looking category 2 lens can block all UV and still leave you squinting into a white glacier all day — and squinting all day is how you finish the trek with a headache and a sunburnt eyelid. You want both: full UV blocking and the right category.
What we would actually put in your bag
About the links below. Some go to Amazon, and as an Amazon Associate we earn from qualifying purchases — at no extra cost to you. It changes nothing about the advice: we tell people to rent down jackets and sleeping bags in Thamel rather than buy them, and we earn nothing when they do. These are the things worth owning.
Category 4 — the specialist option, not the default
Worth it for a glaciated pass, a long crossing on snow, or if you know you are sensitive to glare. Category 4 cuts visible light to 3–8% getting through, and side shields stop the light coming off the snow at your cheekbones. But we should be straight with you: on the EBC and Gokyo trails most people wear category 3 and are fine. One trekker who paid attention on those routes counted three pairs of glacier glasses among hundreds of walkers.
Do not drive in these — not road legal in several countries. And do not buy them out of anxiety. For a standard teahouse route in a normal autumn, category 3 is both the honest answer and the cheaper one.
Compare category 4 glacier glasses →A well-fitting category 3 wraparound
Poon Hill, Mardi Himal, Ghandruk, Langtang, Annapurna Base Camp — and, on the evidence of what trekkers actually report back, Everest Base Camp and Gokyo too. Fit and wrap matter more than darkness, because a pair that seals to your face is a pair you keep on. Polarised is a genuine comfort upgrade on wet rock and lake glare.
You do not need to spend $200 on this. Above about $60 you are mostly buying brand and frame materials, not more protection.
Compare category 3 wraparounds →A spare pair, in the bottom of your daypack
Sunglasses get sat on, dropped down a moraine slope, or left on a windowsill in Dingboche, and there is no shop up there. In fairness, this is a precaution rather than a documented crisis — we went looking and could not find trekkers reporting that a lost pair ruined their trip. But a $20 backup weighs nothing, and the downside of not carrying one is a day of squinting into snow.
Skip it if you are staying low or trekking outside snow season. It does not need to match — it needs to exist.
Compare budget backups →Going high this autumn?
Everest and Annapurna were untouched by the 2026 floods and are running normally. Our guides carry a spare pair for exactly the reason above.
- Everest Base Camp — 14 days · from US$1,650 per person
- Annapurna Base Camp — 7 days · from US$730 per person
What we would not bother with
Since we are the ones telling you to buy something, here is the other half of it.
Ski goggles. Unless you are going above 6,000 m or climbing a peak, they are overkill, they fog on a hot climb, and they are one more thing in the pack. Glasses that fit properly do the job on every teahouse trek in this country.
The $8 pairs in Thamel. Some are fine. Many carry a category marking that has no relationship to the lens in the frame, and there is no way to tell them apart in the shop. It is a strange thing to gamble your eyesight on to save twenty dollars.
Prescription-glasses-plus-clip-on. It works at home; it fails in wind because the clip-on lets light straight in at the sides. If you wear glasses, get prescription sunglasses made before you come, or bring contacts and a proper wraparound.
The one case worth knowing about. A 17-year-old was helicopter-evacuated from Annapurna Base Camp with burned retinas — while carrying sunglasses and factor 50. She had taken the glasses off for a few minutes to slide down a snow slope. That is the realistic risk on a teahouse trek: not the wrong lens category, but the twenty minutes you spend wearing nothing at all.
If it happens anyway
You will know six to twelve hours after the exposure: a gritty feeling like sand under the lids, watering, real pain, and light becoming unbearable. It is frightening and it is almost always temporary — the surface of the eye heals in a day or two.
What helps: get into the dark, take the contacts out and leave them out, cool compresses, painkillers, and do not rub. What does not help: pushing on to the next village in bright snow, which is how a bad day becomes a worse one. Tell your guide immediately — ours carry spare glasses and will rearrange the day around it rather than let you walk through it.
Is category 4 really necessary for Everest Base Camp?
Honestly, usually not. Trekkers who have actually walked it report overwhelmingly that a good category 3 was enough, and one who watched the trail closely counted three pairs of glacier glasses among hundreds of walkers. Category 4 earns its place in deep snow, on a glaciated pass, or if you know you are glare-sensitive. We would rather tell you that than sell you the dearer lens.
Can I just buy sunglasses in Kathmandu?
You can, and there are genuine outdoor shops in Thamel selling real branded stock. The problem is the copies sitting beside them at a tenth of the price with an identical-looking sticker. If you are buying in Kathmandu, buy from an established shop and expect to pay something close to Western prices for the real thing.
Do I need them on cloudy days?
Yes, and this is where most snow blindness actually happens. Cloud scatters ultraviolet rather than stopping it, the glare feels manageable so nobody puts glasses on, and the snow is still throwing 80% of it straight back up at you.
What about children on a family trek?
Children's eyes transmit more UV to the retina than adults', so if anything they need it more. Get a category 3 or 4 pair that actually stays on a smaller face — a strap helps — and be the parent who is annoying about it.
Are polarised lenses worth the extra?
For comfort, often yes — they cut reflected glare off wet rock, rivers and lakes. But polarisation is not UV protection and it is not the category. Treat it as a nice-to-have on top of the two things that matter.
Is this the only gear I should buy rather than rent?
Broadly: buy what has to fit you or touch you — boots, socks, eye protection, a base layer. Rent the bulky expensive things you will use once: down jacket, sleeping bag, and poles if you do not hike at home. That split is in our Nepal gear rental guide.
Keep reading
Questions about a specific trek and what the light will be like on it? Ask us — we walk these trails every season and we would rather tell you to spend less.
The rest of our gear advice. We keep every recommendation in one place at what to buy and what to rent — organised by category, and including the expensive things we think you should rent in Thamel rather than buy. Those carry no buy links, because there is nothing there for us to earn.
Featured image: Grisha Grishkoff via Pexels.
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Written by
Laxman RawalPokhara-based, NMA-certified trekking guides. We’ve led 5,000+ treks across the Annapurna and Everest regions since 1998 — every word here comes from the trail. More from this author →
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