Many believe sunburn risk diminishes significantly after 5 PM. However, sunburn is possible in the late afternoon and early evening, as harmful ultraviolet (UV) radiation remains present until sunset. Understanding UV exposure and influencing factors is important for protecting skin at all times. This requires a comprehensive approach to sun safety beyond traditional midday precautions.
The Science of UV Exposure
Sunburn results from exposure to ultraviolet (UV) radiation, primarily from two types of rays: UVA and UVB. UVB rays are largely responsible for sunburn and contribute to skin cancer risk, while UVA rays penetrate deeper into the skin, causing aging and also contributing to skin cancer. The intensity of UV radiation typically peaks between 10 AM and 4 PM when the sun is highest in the sky. During these hours, UV rays travel a more direct path through the atmosphere, leading to stronger exposure.
As the day progresses, the sun’s angle decreases, meaning UV rays travel through more atmosphere. This increased absorption reduces the intensity of UVB rays, which are more easily scattered and absorbed. However, UVA rays are less affected by atmospheric scattering and remain present throughout daylight hours, even when the sun is lower. While the overall UV Index might be lower after 5 PM, continuous exposure to UVA rays can still contribute to skin damage and premature aging.
Beyond the Clock: Influencing Factors
Several environmental and individual factors increase sunburn risk, even when the sun is not at peak intensity. Geographic location plays a role, with areas closer to the equator experiencing higher UV levels year-round due to the sun’s more direct path. Altitude also affects UV exposure; for every 1,000 meters increase in elevation, UV levels can rise by about 10% to 12% due to less atmosphere. Spending time in mountainous regions late in the day can still pose a significant risk.
Reflective surfaces amplify UV exposure. Water, sand, and snow can reflect UV radiation, increasing the amount that reaches the skin. For instance, fresh snow reflects up to 85% of UV, while dry beach sand reflects about 15% to 18%.
Even on cloudy days, UV radiation can penetrate cloud cover, with up to 90% of UV rays still reaching the Earth’s surface, making sunburn possible despite overcast conditions. Individual skin sensitivity also dictates how quickly one might burn, with fair skin types being more susceptible to UV damage.
Strategies for Skin Protection
Protecting skin from UV radiation requires consistent effort regardless of the time of day. Apply a broad-spectrum sunscreen with an SPF of 30 or higher, as it defends against both UVA and UVB rays. Apply generously to all exposed skin 15 minutes before going outdoors. Reapplication is necessary at least every two hours, or more frequently if swimming, sweating, or toweling off. Even in the late afternoon, if the sun is still visible, using sunscreen on exposed skin is a safe practice.
In addition to sunscreen, protective clothing provides a physical barrier against UV rays. Wearing long-sleeved shirts, long pants, and wide-brimmed hats shields large areas of the body. Tightly woven fabrics offer better protection than loosely woven ones.
Seeking shade, especially during higher UV intensity, can also reduce overall exposure. Planning outdoor activities for early morning or late afternoon, when UV levels are generally lower, is a good strategy to minimize risk.