And, yes, that includes on cloudy days. As Andrea Pfeffer, founder of Pfeffer Sal, explains, “UVB rays which are responsible for burning and tanning are filtered out by clouds and windows, but UVA rays which are responsible for sun damage can still penetrate so if you’re working by a window or taking daily walks, you will still be exposed to them. This is called incidental sun exposure which we still need to protect our skin against.”