Last updated: August 1, 2025
Understanding the UV Index is crucial for residents of Boston, Massachusetts, where the combination of a humid continental climate and seasonal variation in sunlight can lead to significant changes in UV exposure throughout the year. Being aware of the UV levels helps in preventing sunburn and promoting long-term skin health, especially since Boston experiences peak UV Index readings that soar as high as 9 during sunny afternoons in summer. With outdoor activities attracting many to enjoy the city's rich history and beautiful parks, staying informed about UV risks allows Bostonians to protect their skin effectively and enjoy the sunshine safely.
The UV Index reveals a dynamic pattern throughout the day, starting at a mild 1 at 07:00 and steadily rising as the sun reaches its peak. By 10:00, it escalates to a moderate 6, reaching 8 at 11:00 and peaking at an intense 9 from 12:00 to 13:00. This period signifies the greatest caution for sun exposure, making it essential to seek shade and wear protective clothing. As the afternoon unfolds, the index begins to dip, dropping to 8 at 14:00, then declining further to 7 by 15:00, and tapering down to 1 by 19:00. Overall, it’s a day that encourages sun safety awareness, particularly during the midday hours when UV radiation is at its strongest.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 2 | low | 45 min |
| 09:00 | 3 | moderate | 30 min |
| 10:00 | 5 | moderate | 30 min |
| 11:00 | 7 | high | 25 min |
| 12:00 | 8 | very high | 15 min |
| 13:00 | 8 | very high | 15 min |
| 14:00 | 7 | high | 25 min |
| 15:00 | 6 | high | 25 min |
| 16:00 | 4 | moderate | 30 min |
| 17:00 | 2 | low | 45 min |
| 18:00 | 1 | low | 45 min |
| 19:00 | 1 | low | 45 min |
Throughout the year, the UV Index demonstrates significant seasonal changes, particularly peaking in the summer months. Notably, April to August presents the highest risk for UV exposure, with May and June reaching a maximum of 10, categorized as very high risk, where the burn time drops to just 15 minutes. Visitors and residents should be especially cautious during these months, ensuring they wear protective clothing, apply broad-spectrum sunscreen, and seek shade during peak hours. Conversely, the UV Index declines from September onwards, dropping to a low of 2 in December, which indicates reduced risk. It is advisable to remain vigilant year-round, adapting sun safety practices according to the current UV levels to ensure optimal skin protection.
UV Risk Categories
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Boston | 3 | 5 | 5 | 8 | 9 | 10 | 9 | 9 | 7 | 6 | 4 | 2 |
| Chicago UVI | 3 | 4 | 6 | 8 | 9 | 10 | 10 | 9 | 8 | 6 | 4 | 2 |
| Brooklyn UVI | 3 | 5 | 6 | 8 | 10 | 10 | 9 | 9 | 8 | 6 | 4 | 2 |
| New York City UVI | 3 | 5 | 6 | 8 | 10 | 10 | 9 | 9 | 8 | 6 | 4 | 2 |
| Los Angeles UVI | 4 | 6 | 8 | 9 | 10 | 11 | 11 | 10 | 10 | 7 | 5 | 4 |
| Houston UVI | 5 | 8 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 9 | 7 | 5 |