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The Colorado Trail stretches 486 miles through some of the most stunning alpine terrain in North America, but there’s an invisible danger that catches many first-time thruhikers off guard: intense ultraviolet radiation at high elevation. Unlike lower-altitude trails, the Colorado Trail maintains an average elevation above 10,000 feet, with significant portions crossing exposed alpine terrain above treeline. Understanding UV exposure at these heights isn’t just about comfort; it’s a critical safety concern that deserves serious attention before you take your first step.
Why UV Exposure Intensifies at Elevation
UV radiation increases approximately 8-10% for every 1,000 feet of elevation gain. On the Colorado Trail, where you’ll regularly hike between 8,000 and 13,000 feet, you’re exposing yourself to UV levels 30-50% stronger than at sea level. This happens because there’s less atmosphere to filter harmful rays as you climb higher.
But elevation isn’t the only factor amplifying your exposure. Colorado’s geographic location near the 40th parallel means the sun’s rays strike at a more direct angle than in northern states. The state’s famously thin air and low humidity provide even less natural UV filtering. Add in the reflective properties of snow, water, and light-colored granite, and you’re dealing with a compound effect that can double or even triple your effective UV exposure compared to a beach at sea level.
Many beginners assume sun protection is only necessary during summer or on cloudless days. This is dangerously wrong. Up to 80% of UV rays penetrate cloud cover, meaning overcast days still pose significant risk. UV exposure remains a threat from spring through fall, and snow reflection makes it especially hazardous for early-season and late-season hikers tackling high passes.
Understanding the Real Risks
UV damage isn’t limited to painful sunburns, though you’ll certainly experience those if unprepared. Acute exposure can cause photokeratitis (essentially a sunburn of your corneas), severe skin burns that blister and peel, heat exhaustion compounded by sun exposure, and dangerous dehydration as your body works overtime to repair cellular damage.
The long-term consequences are equally serious. Thruhikers spend 4-6 weeks under intense UV bombardment, accumulating damage that can increase skin cancer risk, cause premature skin aging and permanent sun spots, creates vision problems including cataracts, and can compromise your immune system’s effectiveness.
Recognizing Warning Signs
Your body will tell you when UV exposure is becoming dangerous, but you need to recognize the signals before serious damage occurs.
Immediate warning signs include skin feeling hot or tight even in cool temperatures, any redness or pink coloring on exposed skin, eyes feeling gritty, dry, or sensitive to light, and headaches that worsen in direct sunlight. If you notice these symptoms, you need to cover up immediately and seek shade.
Escalating symptoms that require urgent attention include blistering skin, vision becoming blurry or seeing halos around lights, nausea or dizziness combined with sun exposure, and chills or fever developing after sun exposure. These indicate severe UV damage requiring rest, extensive protection, and possibly medical attention.
Essential UV Protection Gear
Successfully managing UV exposure on the Colorado Trail requires a comprehensive protection system, not just a single item.
Sun-Protective Clothing
Your first line of defense is UPF-rated clothing (Ultraviolet Protection Factor). Look for lightweight, long-sleeved shirts like the Zpacks Townshirt and pants with UPF 30 or higher. Many thruhikers resist covering up in warm weather, but proper sun shirts use moisture-wicking fabric that actually keeps you cooler than exposed skin baking in direct sunlight.
Sun hoodies have become extremely popular on high-altitude trails. These pullover shirts, like the OR ActiveIce Spectrum, feature built-in face protection, thumb loops to cover the backs of your hands, and hoods that protect your neck and ears. Brands like Outdoor Research, Patagonia, and REI offer models specifically designed for alpine conditions.
Don’t forget sun gloves or fingerless gloves with long cuffs. The backs of your hands receive constant exposure while hiking with trekking poles, and hand skin is particularly prone to sun damage.
Head and Face Protection
A wide-brimmed hat is non-negotiable. Baseball caps leave your ears and neck exposed to the areas most commonly affected by skin cancer. Look for hats with at least a 3-inch brim all the way around, dark-colored underbrim to reduce reflection up into your face, and breathable, moisture-wicking construction.
Neck gaiters or buffs provide versatile protection. You can pull them up to cover your lower face during exposed ridge walks, wrap them around your neck, or wear them under your hat for additional ear coverage.
Eye Protection
Sunglasses rated for 100% UVA and UVB protection are absolutely essential, not optional. At high elevation, UV damage to your eyes accumulates quickly. Look for wraparound styles that prevent light from entering around the edges, polarized lenses to reduce glare from snow and water, Category 3 or 4 darkness rating for alpine conditions, and secure retention systems so they won’t fly off in wind.
Glacier glasses with side shields offer maximum protection for extended time above treeline, though they may be overkill for sections below 11,000 feet.
Sunscreen Strategy
Even with protective clothing, you’ll have exposed skin that needs chemical protection. For thruhiking, you need a comprehensive sunscreen system.
Choose broad-spectrum sunscreen with SPF 30 minimum (SPF 50+ is better for high altitude). Mineral-based formulas using zinc oxide or titanium dioxide are less likely to run into your eyes when you sweat, though chemical sunscreens may be more water-resistant.
Application technique matters enormously. Apply 15-30 minutes before sun exposure so it binds to your skin, use approximately one ounce (a shot glass full) for full body coverage, and reapply every 90 minutes to two hours, or immediately after swimming or heavy sweating.
Pay special attention to commonly missed spots: tops of ears, back of neck, part line in your hair if visible, tops of feet if wearing trail runners, and backs of hands and wrists.
Lip protection deserves its own mention. Lips have no melanin and burn easily at altitude. Carry SPF 30+ lip balm and reapply frequently throughout the day.
Additional Protective Items
A lightweight umbrella might seem unusual for backpacking, but many Colorado Trail thruhikers swear by them. A small hiking umbrella provides instant shade during breaks, shields you during exposed ridge walks, and doubles as rain protection. Models like the Montbell Travel Umbrella weigh just 3-4 ounces.
Trekking pole attachments let you secure an umbrella hands-free, creating mobile shade as you hike. This setup works brilliantly for long, exposed climbs where you’re moving slowly enough that the umbrella stays positioned overhead.
Timing and Route Strategy
Smart thruhikers adjust their hiking schedule to minimize peak UV exposure. UV radiation is strongest between 10 AM and 4 PM. On particularly exposed sections, consider starting earlier to reach treeline or camp before midday, taking extended breaks in whatever shade is available during peak hours, and resuming hiking in late afternoon when UV intensity decreases.
Study your guidebook to identify highly exposed sections where you’ll be above treeline for extended periods. The Collegiate West route, segments near Kokomo Pass, and the approaches to high passes all require extra preparation and possibly schedule adjustment.
Year-Round Considerations
Spring and fall hikers face unique UV challenges. Snow reflection can increase UV exposure by 80-90%, meaning a cloudy day on a snowfield can deliver worse UV exposure than a sunny day on dirt trail. Early season hikers need glacier glasses and must be even more diligent about reapplying sunscreen to exposed skin.
The combination of cold temperatures and intense UV creates a false sense of security. You won’t feel yourself burning when it’s 45 degrees and windy, but the UV damage is happening just as quickly.
Building Your Protection System
As you prepare for the Colorado Trail, think of UV protection as a layered system where redundancy increases safety. Start with protective clothing as your foundation, add sunglasses and hat for face and eye protection, use sunscreen on all remaining exposed skin, and consider an umbrella for extended exposed sections.
The gear investment is minimal compared to your overall thruhiking budget, but the protection it provides is invaluable. UV damage is cumulative and irreversible, so preventing it in the first place is far better than dealing with the consequences.
Your thruhike should be remembered for stunning alpine vistas and personal achievement, not for painful burns or long-term health consequences. With proper understanding and the right protective gear, you can safely enjoy everything the Colorado Trail offers while keeping your skin and eyes healthy for many adventures to come.