Many people mistakenly believe sunburn is only a risk during peak midday hours, assuming the sun’s rays are too weak by evening. This misconception can lead to inadequate sun protection. While ultraviolet (UV) radiation intensity decreases as the day progresses, UV rays remain present as long as the sun is above the horizon, meaning sunburn is possible after 7 PM.
Understanding Ultraviolet Radiation and Sunburn
Sunburn results from exposure to ultraviolet (UV) radiation. Two primary types of UV radiation reach Earth’s surface and affect skin: Ultraviolet A (UVA) and Ultraviolet B (UVB). UVA rays have longer wavelengths and are associated with skin aging and tanning, and can contribute to sunburn. UVB rays have shorter wavelengths and are the main cause of sunburn, damaging the outermost layers of the skin.
Both UVA and UVB radiation can harm skin cells by damaging their DNA, leading to premature aging and skin cancer. Overexposure to UVB causes the redness and inflammation characteristic of sunburn. While UVA rays are present consistently throughout the day, UVB intensity fluctuates more, being strongest when the sun is highest in the sky. Both types of rays are present whenever the sun is visible.
Factors Affecting Evening Sun Exposure
The intensity of UV radiation in the evening is influenced by several environmental factors. The sun’s angle is a key factor; as the sun gets lower in the sky, its rays travel through more of the Earth’s atmosphere. This increased atmospheric path filters out some UV radiation, particularly UVB, reducing intensity compared to midday. Despite this, UV rays are still present and can cause damage.
Geographic location also plays a role, with areas closer to the equator experiencing stronger UV radiation year-round, even in the evenings, due to the sun’s more direct path to the Earth’s surface. The time of year also impacts UV intensity; summer months have higher UV levels due to the sun’s higher position. Altitude increases UV exposure, as thinner air at higher elevations absorbs less UV radiation, leading to a 10-12% increase in intensity for every 1,000 meters of elevation gain.
Cloud cover can reduce UV levels, but thin or scattered clouds may not significantly block UV rays and can even increase exposure by scattering radiation. Reflective surfaces like water, sand, and snow significantly increase UV exposure by bouncing rays onto the skin. For example, dry beach sand reflects 15-18% of UV radiation, and water reflects about 10%, meaning reflected rays can still cause a sunburn. The UV Index, which measures UV strength, typically declines in the late afternoon and evening but can remain at moderate levels, indicating continued risk.
Strategies for Sun Protection
Protecting skin from UV radiation remains important as long as daylight is present. One effective strategy involves wearing protective clothing, such as long-sleeved shirts and pants made from tightly woven fabrics. A wide-brimmed hat that shades the face, ears, and neck offers additional protection.
Applying broad-spectrum sunscreen with an SPF of 30 or higher to all exposed skin is recommended. Sunscreen should be applied generously at least 15-30 minutes before going outdoors and reapplied every two hours, or more frequently after swimming or sweating. Seeking shade, especially when the UV Index is higher, can significantly reduce exposure. Checking the local UV Index provides a helpful guide for determining risk and necessary precautions, including during evening hours.