Ultraviolet (UV) refers to a type of electromagnetic radiation that has a wavelength shorter than visible light but longer than X-rays. Specifically, UV radiation falls within the wavelength range of approximately 10 nanometers (nm) to 400 nm. It is categorized into three main types based on its wavelength: 1. **UVA (320-400 nm)**: This type of UV radiation penetrates the skin more deeply and is primarily responsible for skin aging and long-term skin damage.