Tanning is the skin’s defense mechanism, triggered when ultraviolet (UV) radiation stimulates the production of melanin, a dark pigment. Whether you can tan in the evening depends entirely on the specific type of UV radiation present as the sun drops toward the horizon. While the sun’s intensity decreases dramatically in the late afternoon, the composition of the light changes, still posing a risk to skin health.
How Ultraviolet Radiation Causes Tanning
Ultraviolet radiation (UV) from the sun is categorized into two main types: UVA and UVB. These rays affect the skin differently, leading to distinct tanning responses. UVB rays have a shorter wavelength, penetrate the epidermis, and are the primary cause of sunburn. Overexposure to UVB stimulates melanocytes to produce new melanin, which results in a lasting tan.
UVA rays have a longer wavelength, allowing them to penetrate deeper into the dermis layer. These rays cause immediate pigment darkening by oxidizing existing melanin and redistributing pigment granules. This darkening is a quick, short-lived tan. UVA exposure also contributes significantly to long-term damage like aging and skin cancer, as both UVA and UVB damage the DNA in skin cells.
Measuring UV Intensity Throughout the Day
The sun’s angle relative to the Earth dictates UV intensity throughout the day. When the sun is directly overhead around solar noon, its rays travel the shortest distance through the atmosphere, resulting in the highest UV Index. As the sun sets, its rays pass at a greater angle through the atmosphere. This increased atmospheric filter absorbs and scatters a significant amount of the high-energy UVB rays.
However, the longer-wavelength UVA rays are not filtered as effectively by the atmosphere, even at low solar angles. While the risk of immediate sunburn from UVB is dramatically reduced in the evening, a considerable amount of UVA radiation is still present.
The tanning potential from new melanin production is low, but the potential for immediate pigment darkening and underlying cell damage from UVA remains. The UV Index primarily reflects the drop in UVB, but it does not fully communicate the lingering presence of UVA.
The Specific Risks of Late-Day UVA Exposure
Although the late-day sun feels milder, the remaining UVA radiation carries significant long-term risks. UVA rays penetrate deep into the skin, affecting cells where most skin cancers originate. This deep penetration accelerates the breakdown of collagen and elastin fibers in the dermis, a process known as photoaging, leading to wrinkles and leathery skin texture.
UVA damage is cumulative over a lifetime, even though it is less visible than a sunburn. Unprotected exposure, even at low intensity, contributes to genetic damage that can lead to basal cell carcinoma, squamous cell carcinoma, and melanoma. Furthermore, UVA exposure can suppress the skin’s immune response, making it harder for the body to fight off damaged cells.
Practical Guidelines for Safer Sun Habits
To protect against UV damage, a consistent routine of sun-safe habits is recommended regardless of the time of day. The primary defense is applying a broad-spectrum sunscreen with a Sun Protection Factor (SPF) of 30 or higher. Broad-spectrum protection filters both the burning UVB and the deeply penetrating UVA rays.
Protective clothing is highly effective, including lightweight, long-sleeved shirts and wide-brimmed hats that shield the face, ears, and neck. Seeking shade, especially during the peak hours of 10 a.m. to 4 p.m., is another effective strategy. Even if you are outside in the evening, reapply sunscreen every two hours, particularly if you are sweating or near reflective surfaces like water or sand.