Sun Protection and Snow Blindness in the Himalaya

At 4,000 to 5,500 m on snow, the sun can hurt in ways you do not expect, and your eyes are the part that suffers first. Wear wraparound sunglasses that give 99 to 100% UV-A and UV-B protection from the first snow, a broad-brimmed hat or a cap with a neck cover, and high-factor sunscreen on every patch of exposed skin, including lips, nostrils and under the chin. The WHO says UV levels rise with altitude because thinner air absorbs less, and that fresh snow and other reflective surfaces raise exposure further. The painful eye condition people call snow blindness is photokeratitis, an inflammation of the cornea, which the WHO describes as reversible and not usually linked to long-term damage, but it can leave you in pain and unable to see for a day or more, at the worst place to lose your sight.

This is general information, not medical advice. If you have an eye condition or take medicines that make you sensitive to sun, ask a doctor before you go. The CDC's Nepal page also tells travellers to be especially careful during summer months and at high elevation.

Why the sun is harsher up high

The WHO's fact sheet says that UV radiation levels increase with altitude as the air is thinner and less UV is absorbed, and that reflective surfaces such as water, sand and fresh snow increase the level further. The CDC's altitude chapter lists increased ultraviolet radiation, with cold and low humidity, among the things that high altitude exposes travellers to. In practice that means that on a snowy pass or a glacier-side viewpoint, you are hit by sun from above and from below. Cloud does not reliably help, because UV passes through thin cloud, and a cool breeze hides the heat while the skin still burns. Routes on which this matters most reach high, bright ground: the Everest Base Camp trek rises to Gorak Shep at 5,164 m and Kala Patthar at 5,545 m, the Annapurna Circuit crosses Thorong La at 5,416 m, and the Langtang Valley climbs to Kyanjin Ri at 4,773 m.

Photokeratitis: what it feels like

The WHO lists photokeratitis and photoconjunctivitis among the acute effects of UV: inflammation of the cornea and the conjunctiva. They are painful and reversible. The usual story is that symptoms appear several hours after the exposure, often in the evening or at night: eyes feel gritty, as if sand is in them, they water, the lids swell, light is painful and vision may blur. It affects both eyes. By morning you may not be able to open them. It heals in a day or two in most cases, but the walking days lost, and the risk of stumbling on a pass with one eye shut, are the real costs. Prevention is cheap; treatment on the trail is little more than rest, shade and patience, and a check by a clinician if the pain is severe or does not settle.

Sunglasses: what to pack

The WHO recommends wraparound-style sunglasses that provide 99 to 100% UV-A and UV-B protection. Look for a label that says so, and for lenses dark enough for snow glare; do not assume a dark lens is a protective one, so check the label and buy from a shop you trust, before you leave home if you can. Wraparound frames or side shields cut light that comes in from the side and from below. Carry a spare pair, because losing a pair on a pass is a classic way to get snow blindness, and a strap keeps them on your head. If you wear prescription glasses, ask your optician about clip-ons or prescription sunglasses, or use contact lenses with sunglasses over them, with care in dust and cold. Keep the case where you can reach it, and put the glasses on before the snow starts, not after your eyes hurt.

Hats, skin and sunscreen

The WHO recommends a broad-brimmed hat to protect the eyes, face, ears and neck, and seeking shade where you can. A cap with a neck flap, a buff over the nose and a light long-sleeved shirt also work. Apply a high-factor, broad-spectrum sunscreen to the face, ears, neck, backs of hands and any other exposed skin, and put more on under the chin and under the nose where reflected light hits. Reapply during the day, especially after sweating. Use a lip balm with sun protection, since lips burn and crack in dry high-altitude air. Sunburn at altitude can be severe, so make reapplying part of every lunch stop. Pack a small tube you can keep in a pocket so that it does not freeze in your bag.

What to do if your eyes burn

Get out of the light. Go to a dark room, cover the eyes with a clean, cool, damp cloth and rest. Do not rub them. Remove contact lenses. Drink fluids and take simple pain relief if you can take it safely. Tell your guide and partners, and plan to stay another day if you cannot see well. If the pain is severe, if you have loss of vision, a very red eye, pus or any injury to the eye, or if symptoms are not improving within a day or two, seek medical help, in a clinic or in Kathmandu. Do not carry on over a high pass half-blind: a partner who guides you on a rope-free but icy slope is a risk for both of you. Our emergency steps guide lists who to call.

The cold and the sun together

High passes combine bright light with cold, and trekkers protect one and forget the other. Your sunglasses fog in a cold start, your sunscreen freezes in a pocket and your hat blows off in wind. Plan for the pass day: sunglasses and sunscreen in an inside pocket where body heat keeps them usable, a hat with a strap or a buff under it, and a spare of each in a partner's bag. Our cold health guide and the packing list cover the rest of the clothing. Snow and high-pass conditions explain when snow cover is most likely, which is when glare is worst.

Sun and altitude illness

Sun exposure and dehydration go together: a day of heat and wind on a bright pass can leave you headachy and drained, symptoms that can be mistaken for or add to altitude sickness. Keep drinking, rest in shade at lunch and do not read every headache as altitude sickness, or dismiss it as a sunburn. Our hydration guide explains how much to drink, and altitude sickness basics lists the symptoms that call for a rest day or a descent.

Partners and sun safety

Partners can remind each other: check each other's faces at lunch for pink skin, remind each other to reapply and carry a spare pair of sunglasses in the group kit. Agree that if someone loses their glasses on a snow section, the group slows down, someone gives them a spare or a shield and nobody mocks the problem. If you want to find people for a high route, look at the Everest Base Camp and Annapurna Circuit partner pages. The altitude and health hub links the rest of the series, and first aid kit for Nepal treks lists the sun and eye items to pack.

A pass-day sun checklist

Put sunscreen on before you leave the lodge, not at the pass. Check that your sunglasses are in an inside pocket, not the pack lid. Carry a spare pair in the group. Wear a hat with a brim or a neck cover and a buff you can pull over nose and cheeks. Put lip balm with sun protection in your jacket. At the first rest stop, check each other's noses and ears for pink skin, and reapply at lunch. After the pass, put the glasses away only when you are in the lodge, not at the first patch of shade, because light bounces off snow even on a cloudy afternoon. If your eyes feel gritty that evening, tell your guide at once and rest them in the dark.