Sunscreen prevents both types of UV rays penetrating the skin surface and causing damage to the skin cells. As well as causing cancer, UV rays can cause sunburn, which dries the skin out and could make it become blistered, and ageing. When undergoing cancer treatment, some treatments and medication cause your skin to dry out. As sun exposure can exacerbate dry skin, it is best to keep it covered and moisturised, especially in the warmer months.