Let’s start with a diagram of the sun’s damaging rays. This graphic shows the different wavelengths. Smaller wavelengths mean more waves hitting you. Imagine ocean waves coming every second at the shore. It would wear it away. So it is with sun rays. the shortest wavelength beats on us harder.

However, the shorter wavelength interval rays, (let’s call them shortwave now, as is commonly used), in general don’t penetrate as deep into the human skin. UVC waves would kill us almost immediately, but don’t reach the earth. However, don’t sunbathe on the moon, it’s not a good idea, as it doesn’t have a protective air layer. (More on that elsewhere) UVB waves are shorter than UVA. UVB damages our upper layer, via sunburn. UVB goes deeper, damaging our membranes, and is more usually associated with cancer. One way to remember all this is the letters B and A . Think uvB for Burn, and uvA for Aging and cAncer.