The eye burn you won't feel until midnight

Quick answer: Wear wraparound sunglasses with 100 percent UV protection, and wear them on cloudy days too. Cover every inch of skin you can, and put mineral sunscreen on what's left.

You take your sunglasses off at the summit to eat a sandwich. Twenty minutes, maybe thirty. The sky's overcast, the snow's bright but not painful, and you feel fine on the way down. You feel fine at the trailhead. You feel fine at dinner.

Around midnight your eyes start to feel like someone poured sand under the lids.

That's snow blindness, and the delay is what catches people. The medical name is photokeratitis. It's a sunburn on the surface of your eye, and like a skin burn, you don't feel it while it's happening. The pain arrives six to twelve hours later, usually when you're a long way from help or a very long way from sleep.

Why snow and altitude stack the deck

Fresh snow bounces back most of the UV that hits it. You're getting hit from above and from below, including the under-chin, under-nose, and under-brim spots that never see sun in July. Altitude adds to it, because there's less atmosphere to filter the light as you climb.

Clouds don't save you. UV passes through thin overcast, and the flat white light makes people pull their glasses off because it doesn't feel bright. That's the mistake. Glare is your comfort gauge, and it lies.

What it feels like and what to do about it

Symptoms are gritty, burning eyes, heavy tearing, light sensitivity, swollen lids, and sometimes a headache. It looks frightening. It usually clears up in a day or two once the surface of the eye heals. That's general education, not a diagnosis, so use judgment.

If it happens:

• Get out of the light. A dark tent or a dark room is the treatment.
• Take contacts out and leave them out.
• Lay a cool, damp cloth over closed eyes.
• Use plain artificial tears if you have them.
• Don't rub. It feels like the right move and it's the wrong one.

See a doctor if the pain is severe, your vision is blurry or doesn't return to normal, or it isn't clearly improving within a day or two. If you're remote and can't see to travel, that's a different problem. Stay put, stay warm, and send someone for help if you're not alone. It's also a fast way to end up in the situation covered in what to do in the first hour you're lost in the woods.

The eye gear that works

You need three things from a pair of glasses: full UV blocking (look for "100% UV" or "UV400"), a wraparound shape, and a dark enough lens.

• Lens darkness. Category 3 lenses handle most winter days and run roughly $30 to $150. Category 4 lenses are made for glaciers and extreme altitude, run $60 to $250, and are far too dark for driving. Don't wear them behind the wheel on the way home.
• Side coverage. Light comes in around the edges and reflects off the inside of the lens. Glacier-style removable side shields, or a close wraparound frame, fix that. Side shields run about $10 to $20 if you need to add them.
• A retention strap. Five to ten dollars. Losing glasses in deep snow is how a good day becomes a bad one.
• Goggles for wind or snowfall. Ski-style goggles with UV-blocking lenses run $40 to $150 and fog less if you keep them off your forehead when you're working hard.
• A cheap backup pair. Fifteen to twenty dollars, zipped into a different pocket than your main pair. It weighs nothing.

Cheap gas-station sunglasses are the trap. Dark tint with no UV blocking makes your pupils open wider, which lets in more damaging light than no glasses at all. Check the label, not the shade.

The slit goggle you can build in ten minutes

If you lose your glasses, make a pair. Cut a strip of cardboard, tough bark, or flexible plastic long enough to wrap across both eyes. Cut a narrow horizontal slit for each eye. Tie it on with cord or tape it to a hat. You'll see a sliver of the world, and your eyes will get a fraction of the light. It's ugly. It works. Keep a foot of duct tape wrapped around a water bottle or trekking pole and you've already got half the kit.

Skin: where people actually burn

The usual mistakes are all small places. Nostrils. Under the chin. The rims of the ears. The back of the neck below the hat. The part in your hair. Eyelids. Lips, which get less melanin protection than the rest of your face and crack in wind and cold, giving the sun an easy way in.

Cover what you can with fabric. A wide-brim or neck-flap hat, a neck gaiter pulled over the nose, and gloves handle most of it for about $50 total. Use an SPF 30 lip balm (a few dollars) and reapply it every time you eat or drink.

Mineral sunscreen for snow country

Sunscreen still matters on a cold day. Sun damage is a proven cause of skin cancer, and any broad-spectrum SPF 30 or higher, worn every day, beats skipping it. Reapply every two hours, and after heavy sweating.

We recommend mineral sunscreen, the kind built on zinc oxide or titanium dioxide. They sit on top of the skin and cover the full spectrum. In 2019 the FDA proposed those two as the only filters generally recognized as safe and effective, and asked for more safety data on the rest. FDA studies published in JAMA in 2019 and 2020 found common chemical filters, including oxybenzone and avobenzone, absorbed into the bloodstream. FDA and dermatologists still consider approved chemical sunscreens safe and effective. Mineral is simply our pick, and it's gentler on sensitive skin.

The trade-off is a white cast, and cold makes mineral formulas thicker and harder to spread. Tinted versions help with the first. For the second, keep the tube in an inside pocket against your body so it stays workable.

Good options: EltaMD UV Physical SPF 41 (tinted), Blue Lizard Sensitive Mineral SPF 30, Badger Clear Zinc SPF 30, and Neutrogena Sheer Zinc SPF 50.

If you're carrying in snow country

If you hunt in winter or carry a firearm for protection in the backcountry, glare and squinting cost you more than comfort. Tired, sun-battered eyes make it harder to follow the fourth rule: know your target and what's beyond it. Snow hides background, flattens depth, and plays tricks with distance.

The four rules don't bend for cold weather: treat every firearm as loaded, never point it at anything you aren't willing to destroy, keep your finger off the trigger until your sights are on target and you've decided to shoot, and be sure of your target and what's behind it. Good eye protection is part of that discipline. Use shooting-rated glasses or goggles where they're appropriate.

Lawful ownership and carry are a right, and with that right comes the responsibility to train for it. A first firearms class taught by a qualified instructor is the place to start, and nothing replaces it. Lock firearms away from children at home and at camp. If kids are around, teach them what to do if they find a gun. Laws on carry, transport, and hunting vary by state, province, and city. Nothing here is legal advice, so check local law and talk to a qualified attorney or instructor.

Take a class before you need it

A wilderness first aid course, usually a weekend and a couple hundred dollars from a qualified instructor, teaches you to recognize snow blindness, cold injury, and altitude trouble before they're emergencies. You can't learn the hands-on parts from an article.

Pack the glasses before the stove. Put the spare in the lid pocket. And when you stop on that summit for lunch, leave them on and eat with your sunglasses on. Nobody has ever regretted it at midnight.