why you need spf indoor?

cz UV rays can go through the windows 🤔

Short answer: UVA rays may pass through windows and cause premature ageing (UVB rays, which cause sunburn, can't). If you're thinking about not wearing sunscreen indoors, consider how far from the windows are you. If close, you should use sunscreen with sufficient PA protection.

Depending on where you are on earth, the size of your window and the UV index, you may still need to use it indoors. I live in a tropical country, if I were at home and all my windows are open and I like sitting next to it, I would put sunscreen once in the morning. A lot of the UV rays has been dispersed so I don’t worry so much about reapplying unless I was sweating. If I were living somewhere where it is winter, and the UV index is 0-1, I would skip it. If I was in a tropical country and it was night time, or late evening when the index dips below to 2 I would skip it. If I was in a tropical country and I leave my home at dawn, stayed inside a building with no windows, and then get back at dusk, no sunscreen. I usually just use sunscreen once a day out of habit 😄

UV rays can still pass especially on the windows