In comparison to the scorching sun of summer, winter days appear dimmer. Many assume that there is less UV radiation during winter and therefore neglect their skin’s protection. However, in reality, people should be more cautious during winter because the thin cloud layer causes just as much damage as during summer. Understanding the characteristics of UV radiation is crucial in devising effective skincare routines.
Ultraviolet A (UVA) has a wavelength of 315-400 nm and can penetrate through clouds and glass, reaching the skin’s dermis layer. UVA causes skin aging and the formation of wrinkles, making it the primary cause of skin damage. On the other hand, Ultraviolet B (UVB) has a wavelength of 280-315 nm and is absorbed by the ozone layer. UVB causes sunburn, skin redness, and pain and is the most carcinogenic of the three types. Lastly, Ultraviolet C (UVC) has a wavelength of 100-280 nm and is the shortest and most dangerous of the three but is blocked by the ozone layer, making it less harmful to humans.
Therefore, UVA and UVB require the most attention. Both damage collagen, accelerating skin aging. In the past, UVA was considered less harmful than UVB, but recent studies found that it has a direct correlation to skin cancer. UVA can penetrate the skin without causing sunburn but can generate highly reactive chemical intermediates, hydroxyl and oxygen radicals, which destroy DNA. The Sun Protection Factor (SPF) measures UVB intensity, but it cannot measure UVA’s redness of the skin (erythema), so other measures such as PA, PFA, IPD, and PPD are used. When purchasing sunscreen, it is crucial to look for both UVA and UVB protection indices.