UVB, or Ultraviolet Burning, are short wave solar rays measuring 290-320 nanometers. It stimulates the production of essential Vitamin D in our bodies. Considered the cause of sunburn, they are also thought to be the main cause of basal and squamous cell carcinomas, and to highly contribute to the cause of melanoma. UVA, or Ultraviolet Aging, are long wave solar rays of 320-400 nanometers.
They are not fully blocked by the ozone layer and the remaining rays aid photosynthesis for plants and trees to process sugars for food when they extract carbon dioxide from the atmosphere. Over 90% of the rays reaching the earth from the sun are UVA. The bad news about UVA rays is that it penetrates the skin deeper than UVB and can cause damage to the collagen and elastin in the dermis. UVA causes the fine lines and wrinkles of photoaging, pigmentation marks, and in the long term, contributes to the occurrence of skin cancer, especially melanoma. While UVB does not penetrate through glass and water, UVA can, making it more dangerous. It is also present in fluorescent lighting. The highest exposure hours in the day for these rays is 10 AM-4 PM, making these the most important hours in sun exposure avoidance practices; sunscreen is a major part of a comprehensive sun protection program.
