Skiing Injuries: ACL, Skier’s Thumb, Helmets, Cold and Altitude

This article contains affiliate links: if you buy through them we may earn a commission, at no extra cost to you. Learn more.

It’s 3:40 on the last afternoon of the trip. The light has gone flat, the snow has turned to chopped-up piles, and somebody says the words every ski family knows: one more run. Halfway down, a ski catches, a binding doesn’t let go, and a knee twists the wrong way. Skiing has its own set of injuries, from the ACL and “skier’s thumb” to head knocks, tree wells, frostbite and altitude sickness. Here is each one in plain language, what lowers the risk, and the signs that mean “get it checked”, for every skier from ski school and high school racing to college, the World Cup and the weekend trip.

This page is general information, not medical advice. If you’re hurt, see a sports medicine doctor, physical therapist (PT) or certified athletic trainer (AT); on the mountain, ski patrol is your first call. For the bigger picture of the sport, start at our skiing hub.

How risky is skiing?

Less risky than its reputation, but not risk-free. The American Academy of Orthopaedic Surgeons (AAOS) cites U.S. Consumer Product Safety Commission figures of more than 76,000 skiing injuries treated in 2018. A 2026 meta-analysis of 43 studies of recreational skiers and snowboarders found a pooled rate of 1.9 injuries per 1,000 skier-days, and 3.8 per 1,000 days for amateur alpine skiing, with big differences between studies. Falls cause most of them, and arms and legs take the hits. Better boots and bindings have cut overall injury rates by more than half since the 1970s; knees are the part that hasn’t kept up.

Knee injuries and the ACL

The knee is the most common injury site in recreational skiing, about a third of all injuries in an Austrian study, and in that study’s hospital cases the anterior cruciate ligament (ACL) was involved in every knee injury, often with the MCL or meniscus too. Long, stiff boots protect the shin but pass twisting forces up to the knee. Researchers who studied more than 1,400 ACL injuries in skiers identified two classic patterns: the “phantom foot”, when a skier falls back between the skis and the tail of the downhill ski levers the knee, and the boot-induced injury, a hard landing on the tails that pushes the shin forward. You may hear a pop, feel the knee give way, and see it swell within hours (AAOS describes the same signs for any ACL tear).

A 2025 systematic review of 27 studies listed what raises the risk: being female, lower skill, risk-taking, older age, worn boot soles, and especially bindings that are set wrong (in some studies the binding failed to release in up to 96% of ACL cases). Icy, grippy and fresh snow all carried higher risk than soft spring snow.

• Have bindings set by a trained shop technician every season, and after any change in weight, ability or boots. The same researchers list “if you know your DIN you can set your own bindings” among skiing’s myths: setting and testing release takes calibrated tools. AAOS says bindings should meet ASTM standards.
• Learn the ACL “danger positions”. In a study of 20 ski areas, patrollers and instructors who watched video training on how ACL injuries happen had 62% fewer serious knee sprains, with no drop at areas that skipped it. Key ideas: don’t fully straighten your legs when you fall, keep arms forward and feet together, and don’t try to get up until you’ve stopped sliding (racers’ version: “when you’re down, stay down”).
• Neuromuscular training for young racers. In Swedish ski high schools, a program focused on core stability and doing every exercise equally well on both legs cut ACL injuries from 8.1% of students to 3.9%. More on this on our ski training page.

Skier’s thumb

Fall with your hand strapped to a pole and the pole can bend your thumb back and sideways, spraining or tearing the ulnar collateral ligament (UCL) at the base of the thumb. AAOS calls it “skier’s thumb” for that reason. Signs: bruising, swelling and tenderness at the base of the thumb on the index-finger side, and a weak or wobbly pinch. AAOS says even a mild thumb sprain should be checked by a doctor if it doesn’t improve quickly, because a complete tear can leave the joint unstable; treatment ranges from a splint or cast to surgery for severe tears. AAOS also lists shoulder dislocations and fractures from falling on an outstretched arm.

Head injuries, concussion and helmets

Head injuries are less common than knee injuries but the most serious. The evidence on helmets is strong: a meta-analysis in the Canadian Medical Association Journal found skiers and snowboarders with a helmet had about 35% lower odds of a head injury (and lower still in children under 13), with no increase in neck injuries. An evidence-based review for trauma surgeons made it a top-level recommendation that all recreational skiers and snowboarders wear helmets. Skiers listened: the National Ski Areas Association (NSAA) reports helmet use rose from 25% in 2002/03 to 90% in 2023/24, and close to 100% in children 9 and under.

Helmets have limits: a Norwegian study saw their protective effect shrink between 2002 and 2011 as skiing trends changed. NSAA’s line is the right one: wear a helmet, but ski as if you weren’t wearing one.

Concussion: recognize it and stop skiing. The CDC’s HEADS UP program is clear: anyone who may have a concussion stops for the day and doesn’t go back until a health care provider clears them. Watch for a dazed look, confusion, clumsiness, headache, dizziness, nausea, blurry vision or feeling foggy. Call ski patrol or 911 for the CDC’s danger signs: one pupil larger than the other, a headache that gets worse, slurred speech, weakness or numbness, repeated vomiting, seizures, increasing confusion, or loss of consciousness. The 2022 Amsterdam consensus recommends relative rest for the first 24–48 hours, then a step-by-step return, and AMSSM says there is no same-day return to sport after a diagnosed concussion.

Collisions and the Responsibility Code

Hitting a tree, a lift tower or another skier is how many of the worst ski injuries happen. NSAA’s 10-point Your Responsibility Code is the rulebook for avoiding them. The points that prevent the most collisions: always stay in control and be able to stop or avoid people and objects; people ahead of or below you have the right of way; stop only where you’re visible from above; look uphill before you start down or merge onto a trail; and don’t ski or ride lifts impaired by alcohol or drugs. If you’re in a collision, share contact information with the other person and a ski area employee. Our skiing rules page covers the whole code.

Tree wells and deep snow

On powder days the danger is quiet. A tree well or deep-snow immersion accident happens when a skier falls, usually headfirst, into the loose snow around a tree or into deep unconsolidated snow, can’t move, and suffocates. NSAA calls it snow immersion suffocation (SIS), and its main advice is short: always ski or ride with a partner within sight, close enough to dig fast. In the trees, look at the gaps, not the trunks (NSAA points skiers to deepsnowsafety.org).

Leaving the resort boundary is a different sport: avalanche terrain. Avalanche.org notes avalanches kill 25 to 30 people a winter in the U.S. and that most buried people have less than 15 minutes. Backcountry skiers carry a transceiver, probe and shovel, take a course and practice rescue with partners; see the safety section of our ski wearables page.

Cold injuries: frostbite and hypothermia

Chairlifts add wind to cold. The National Weather Service gives an example: at 0°F with a 15 mph wind, the wind chill is -19°F and exposed skin can freeze in about 30 minutes. The American College of Sports Medicine (ACSM) calls for closer watching of athletes at wind chills below -18°F (-27°C). Frostbite most often hits the nose, ears, cheeks, chin, fingers and toes. The CDC describes red, painful skin first, then white or grayish-yellow skin that feels firm, waxy or numb. Get inside, remove wet clothing, and warm the area gently in warm (not hot) water; don’t rub it, and don’t use a fireplace, heat lamp or heating pad. Hypothermia signs are shivering, exhaustion, confusion, fumbling hands, slurred speech and drowsiness; the CDC notes it can happen even above 40°F when someone is chilled by sweat or wet clothing. A body temperature below 95°F is a medical emergency. With kids, check cheeks, ears and fingers on every lift ride.

Altitude sickness

Many Western resorts sit high: the CDC’s Yellow Book notes lodging at about 8,150 ft in Vail and 9,600 ft in Breckenridge, and says acute mountain sickness (AMS) affects about 25% of visitors sleeping above 8,000 ft in Colorado. It feels like a hangover: headache plus loss of appetite, dizziness, tiredness or nausea, usually 2–12 hours after arriving, often after the first night. Children are as susceptible as adults. The CDC advises avoiding going from low elevation to sleeping above 9,000 ft in one day, keeping exercise mild and skipping alcohol for the first 48 hours, and seeing a doctor before the trip if you have heart or lung disease, sleep apnea or sickle cell trait. Get help and go down for confusion, stumbling or drowsiness (possible HACE) or breathlessness at rest and a cough (possible HAPE), or if symptoms get worse while resting. Sun at altitude is its own hazard: see ski day.

Gear that helps

A certified snow helmet that fits is the one piece of gear with strong evidence behind it. The Smith Mission MIPS and the lower-priced Giro Ledge MIPS both use MIPS, a liner system the makers say reduces rotational forces in angled impacts. Disposable HotHands warmers are cheap insurance for cold fingers. After a knee injury, ask your PT whether a sleeve like the Bauerfeind GenuTrain fits your rehab.

When to see a sports medicine doctor, PT or athletic trainer

• Right away (ski patrol / 911): any concussion danger sign, a possible broken bone, a joint out of place, neck or back pain after a fall, numbness or tingling, suspected hypothermia, or altitude symptoms with confusion or breathlessness at rest.
• Within a day or two: a pop and swelling in the knee, a knee that gives way, a thumb that’s swollen or weak to pinch, a suspected concussion, or skin that stayed white, waxy or blistered after warming.
• Soon: pain that keeps you off your skis for more than a few days, swelling that won’t settle, or a child who limps after a ski week.

Return to skiing is a process, not a date: walking, then strength and balance work, then easy groomers, then speed and terrain, each step without pain or swelling, and signed off by the person treating you. Look after the basics on our ski recovery page. Snowboarders have their own injury patterns; see snowboarding.

Skiing injuries: FAQs

What is the most common skiing injury?

Knee injuries, and the ACL in particular. In recreational skiers the knee accounts for about a third of all injuries. Skier’s thumb, shoulder injuries and head injuries follow. Falls cause most injuries.

Do ski helmets really work?

Yes. A meta-analysis found about 35% lower odds of head injury with a helmet, more in children, and no extra risk of neck injury. Helmets have limits at high speed, so skiing in control still matters most.

Can I adjust my own ski bindings?

It’s not recommended. Setting release values properly needs a trained technician, your weight, height, boot sole length, age and skier type, plus calibrated testing. Bindings that don’t release are a major ACL risk factor, so have a shop set and test them each season.

What is a tree well and how do I stay safe?

It’s the deep, loose snow around the base of a tree. Falling in headfirst can trap you and cause suffocation. Ski the trees with a partner who keeps you in sight, steer for the gaps, and stay clear of tree bases on deep-snow days.

How do I know if it’s altitude sickness?

A headache within the first day or so at a high resort, plus poor appetite, nausea, dizziness or unusual tiredness, is typical. Rest, don’t go higher, and skip alcohol. Confusion, stumbling, or shortness of breath at rest are emergencies: get medical help and go down.