There is typically no need to wear sunscreen when indoors, as the risk of sun exposure is low. If you are spending a lot of time by a window with direct sunlight you might want to think about sun protection, though clothing may be sufficient and sunscreen won’t usually be necessary.
To explain the risk, it is important to understand UVR. Solar UVR (Ultraviolet radiation) is invisible energy produced by the sun. The two types of UVR that reach the earth are UVA and UVB. UVA primarily contributes to skin ageing but also increases skin cancer risk, whereas UVB is the major cause of sunburn and increased risk of developing skin cancer. UVB is typically blocked by glass, and certain types of glass can reduce UVA, for example laminated glass eliminates UVA completely.
While UVR exposure through windows presents minimal risk, if the UV level is forecast to be 3 or above and you are going to be outside intermittently during the day, for example to carry out chores like hanging out the washing, then sun protection, including sunscreen use, should be incorporated into your morning routine.
Remember to check the UV and when it’s 3 or higher and you are heading outdoors to use five forms of sun protection – slip on clothing, slop on a broad-spectrum water resistant sunscreen with an SPF30 or higher, slap on a broad-brimmed hat, seek shade and slide on sunglasses.