UVB rays: They are stopped by the epidermis. They stimulate the skin’s defence mechanisms but at higher doses, they are also responsible for sunburn. UVA rays: They are even more aggressive. They penetrate into the deep layers of the skin and lead to premature ageing (wrinkles, dark spots). In the long term, these two types of rays can irreversibly alter the DNA and contribute to the development of skin cancers. Other effects are also observed. When combined with certain medications taken orally or applied to the skin, UV rays can trigger a photosensitive reaction leading to redness and blistering on exposed areas. Effective prevention requires optimal UVB/UVA protection.