UV Index in Colorado (CO)
Colorado has an average annual UV index of 6.5, classified as High — 1.5 points above the national average of 5. UV levels peak in July with an average of 11.3, reaching Extreme levels, and drop to 2.1 in December. During peak months, unprotected fair skin can burn in as little as 9 minutes. SPF 50+ sunscreen, protective clothing, and shade are strongly recommended. Colorado has 7 months per year with High or above UV levels. UV ranges from 6.4 in Fort Collins to 7.7 in Aspen.
Monthly UV Index by City in Colorado
The heatmap below shows the monthly average UV index for 7 cities in Colorado. Colors range from green (low UV, 0-2) through yellow (moderate, 3-5), orange (high, 6-7), red (very high, 8-10), to purple (extreme, 11+). Hover over any cell to see the exact value.
| City | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Avg | Peak |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Aspen | 3 | 5 | 7 | 9 | 11 | 12 | 12 | 11 | 9 | 6 | 4 | 3 | 7.7 | June |
| Denver | 3 | 4 | 6 | 8 | 10 | 11 | 11 | 10 | 8 | 5 | 3 | 2 | 6.8 | June |
| Colorado Springs | 3 | 4 | 6 | 8 | 10 | 11 | 11 | 10 | 8 | 5 | 3 | 2 | 6.8 | June |
| Aurora | 3 | 4 | 6 | 8 | 10 | 11 | 11 | 10 | 8 | 5 | 3 | 2 | 6.8 | June |
| Boulder | 3 | 4 | 6 | 8 | 10 | 11 | 12 | 10 | 8 | 5 | 3 | 2 | 6.8 | July |
| Pueblo | 3 | 4 | 6 | 8 | 10 | 11 | 11 | 10 | 8 | 5 | 3 | 2 | 6.8 | June |
| Fort Collins | 2 | 3 | 6 | 7 | 9 | 11 | 11 | 10 | 8 | 5 | 3 | 2 | 6.4 | June |
Sun Protection Recommendations for Colorado
Based on the peak UV index of 11.3 (Extreme) during July, here are the recommended sun safety measures for Colorado residents and visitors:
Extreme UV — Extreme risk. Unprotected skin and eyes can burn in minutes.
- Apply SPF 50+ broad-spectrum sunscreen every 60-90 minutes
- Wear full protective clothing, hat, and UV-blocking sunglasses
- Avoid the sun between 10 AM and 4 PM
- Stay in the shade as much as possible
- Take all precautions — UV at this level is dangerous
- White sand, water, and high altitude amplify exposure
Recommended sunscreen: SPF 50+ (reapply frequently)
Estimated Sunburn Times in Colorado (July Peak)
Approximate time to first sunburn at peak UV (11.3) without sunscreen, by skin type:
| Skin Type | Description | Time to Burn | Vitamin D Time |
|---|---|---|---|
| Type I | Very Fair | 6 min (high risk) | ~3 min |
| Type II | Fair | 9 min (high risk) | ~3 min |
| Type III | Medium | 18 min | ~4 min |
| Type IV | Olive | 27 min | ~7 min |
| Type V | Brown | 35 min | ~9 min |
| Type VI | Dark Brown/Black | 44 min | ~11 min |
In Colorado, sufficient vitamin D can be produced with just 5-10 minutes of midday sun exposure on arms and face during summer months.
Seasonal UV Patterns in Colorado
Colorado's UV index follows a seasonal pattern, with the lowest levels in December (UV 2.1) and the highest in July (UV 11.3). The seasonal swing of 9.2 UV points means sun protection needs change significantly throughout the year. Here are the state-average UV levels by month:
Summer months in Colorado consistently reach Very High or Extreme UV levels. Outdoor workers, athletes, and beachgoers should take extra precautions from May through September.
How Colorado Compares to Other States
Below is a comparison of Colorado with five states that have similar average UV index levels. Understanding how your state compares helps put your sun exposure risk in context.
| State | Avg UV | Level | Cities |
|---|---|---|---|
| Colorado (CO) | 6.5 | High | 7 |
| Utah (UT) | 6.5 | High | 6 |
| Louisiana (LA) | 6.3 | High | 5 |
| California (CA) | 6.8 | High | 10 |
| Texas (TX) | 6.8 | High | 10 |
| Mississippi (MS) | 6 | High | 5 |
UV Index in Neighboring States
Compare UV levels with states near Colorado:
Skin Cancer Risk Factors in Colorado
UV radiation is the primary environmental risk factor for skin cancer. While the UV index in Colorado is only one factor, understanding cumulative exposure is important. Key risk factors include:
- Cumulative UV exposure — total lifetime sun exposure, especially sunburns before age 18
- Skin type — fair skin (Types I-II) has significantly higher risk
- Geographic location — Colorado's high UV levels increase baseline risk compared to northern states
- Altitude — higher elevations increase UV exposure significantly
- Outdoor occupation/hobbies — agricultural workers, construction workers, golfers, runners, and beach visitors accumulate more exposure
- Tanning bed use — artificial UV exposure dramatically increases risk
The American Academy of Dermatology recommends annual skin checks for everyone, with more frequent screenings for those with multiple risk factors. Early detection dramatically improves outcomes for all types of skin cancer.
Check UV for Your City
Use our UV index lookup tool to find your specific city in Colorado, or browse all 50 states ranked by UV index to compare UV levels across the country. For today's live UV forecast, check the EPA UV Index API with your zip code.