The common belief that sun exposure after 4 PM is harmless is a misconception that can lead to unprotected time outdoors. Tanning is the skin’s protective response, involving the production of the pigment melanin, triggered by ultraviolet (UV) radiation from the sun. The presence of UV light is the sole requirement for this biological process to occur. As long as the sun is above the horizon, the potential for tanning and sun damage remains. This article explores why the sun still poses a risk in the late afternoon and outlines necessary precautions for sun safety.
Can Tanning Occur in the Late Afternoon
Tanning and sunburn can both happen at 4 PM because the sun is still emitting ultraviolet radiation. The intensity of the UV rays significantly decreases after solar noon, which is typically between 12 PM and 2 PM. Despite this reduction, UV radiation does not vanish until sunset, making late-afternoon exposure a cumulative risk factor for skin damage.
Many people mistakenly associate the feeling of heat with the risk of burning, believing that cooler, late-day temperatures mean lower UV risk. However, UV radiation is distinct from the visible light and infrared radiation that primarily cause the sensation of warmth. Since tanning is a biological reaction to UV exposure, the process can be initiated anytime the skin is exposed to the sun’s rays.
Understanding Daily UV Fluctuations
The varying intensity of the sun’s rays throughout the day is dictated by the solar angle, which is the height of the sun in the sky. When the sun is directly overhead around midday, the UV rays travel the shortest distance through the atmosphere, resulting in peak intensity. As the afternoon progresses and the sun sinks lower, its rays must pass through a greater thickness of the Earth’s atmosphere, which filters and scatters more of the radiation.
This atmospheric filtering does not affect all UV types equally. It is particularly effective at blocking UVB rays, which are the primary cause of sunburn and vitamin D production. Consequently, UVB intensity drops off steeply after 2 PM. Conversely, UVA rays, which penetrate deeper into the skin and are responsible for tanning and premature aging, remain relatively constant during all daylight hours.
The late afternoon is characterized by a higher ratio of UVA to UVB radiation compared to the midday peak. While the immediate risk of a quick sunburn may be lower at 4 PM, the skin is still being exposed to potent UVA rays. These rays contribute to long-term cellular damage and photoaging, and UVA stimulates the existing melanin, leading to immediate darkening.
Essential Sun Protection Guidelines
Because a significant level of UV radiation is still present in the late afternoon, year-round sun protection remains a necessary practice. A broad-spectrum sunscreen with a Sun Protection Factor (SPF) of 30 or higher should be applied generously to all exposed skin, even when heading out after 4 PM. It is important to reapply this protection every two hours, or more frequently if swimming or sweating.
A useful tool for assessing risk is the UV Index, which measures the strength of ultraviolet radiation on a scale of 0 (Low) to 11+ (Extreme). Checking the daily UV Index forecast can help determine if extra precautions are needed, as anything in the moderate range (3-5) and above still requires protective measures.
Protective clothing is an effective defense against late-day UV exposure. Wearing a wide-brimmed hat and sunglasses with UV-blocking lenses provides physical barriers against the sun’s rays. Loose-fitting garments made from tightly woven or darker-colored fabrics offer superior protection compared to light materials. Seeking shade when possible, especially if your shadow is shorter than your height, is a simple way to minimize direct exposure throughout the day.