The earth's movement around the sun is elliptical, not circular. This means that during winter, the world is closer to the sun, resulting in more intense solar radiation. Although the air temperature drops, the sun's ultraviolet (UV) radiation does not diminish significantly. These UV rays are the leading cause of skin damage. They are categorized into UVA and UVB rays, each with its unique impact on the skin.
UVA rays, which comprise 95% of the UV radiation reaching the earth's surface, can penetrate the skin more deeply. They are less dependent on the season and are consistently strong throughout the day. UVA rays are primarily responsible for premature skin aging and are a crucial contributor to skin cancer.
UVB rays, on the other hand, vary by season, location, and time of day. They are most potent between 10 a.m. and 4 p.m. and are more prevalent during the summer. However, during winter, UVB rays can reflect off snow, leading to increased UV exposure. These rays cause sunburn and are directly responsible for most skin cancers.
During winter, the atmosphere and ozone layer absorb less UVB radiation, meaning more reaches the earth's surface. Snow can mirror up to 80% of UV radiation, almost doubling the exposure. This reflection is particularly damaging on the often-neglected underside of the chin and nose.
The cold, dry winter air can also impair our skin's barrier function, leading to increased water loss from the skin or transepidermal water loss (TEWL). This can leave the skin more vulnerable to UV-induced damage. Furthermore, because people tend to bundle up in the winter, areas left exposed, like the face and hands, are more susceptible to UV damage.
The scientific evidence of the winter sun's harm to our skin underscores the importance of year-round sun protection. Wearing broad-spectrum sunscreen, which protects against UVA and UVB rays, is crucial even on cloudy winter days. At most, up to 80% of UV rays can still penetrate the clouds. Additionally, wearing sunglasses and protective clothing, as well as seeking shade, can further reduce UV exposure. Regularly applying a moisturizer can help maintain the skin's barrier function and prevent TEWL.
Despite the chill in the air, the risk of UV radiation remains. By understanding the science behind this, we can adopt more comprehensive skincare strategies to protect our skin, not just in the heat of the summer but also in the crisp chill of winter.