Ultraviolet rays, or UV rays, are a type of electromagnetic radiation emitted by the sun. They have shorter wavelengths than visible light, making them invisible to the human eye. UV rays are categorized into three types: UVA, UVB, and UVC, with UVC being the most harmful but mostly absorbed by the Earth's atmosphere. These rays play a crucial role in the production of vitamin D in the skin, which is essential for bone health. However, excessive exposure to UV rays can lead to skin damage, sunburn, and an increased risk of skin cancer. Therefore, protection from UV rays, such as using sunscreen, is important.