Q: I work in the kitchen (hot and smoky) for 4-6 hours, cycling to work back and forth 40 minutes (between 10 am to 3 pm). I heard spf 50 will do harm for your face but I also heard spf 25 is no use, you just have to put it again after a few hours. any opinion is welcome. serious answers only, please.
A: Think of an SPF as a time-extender for sun exposure. If it normally takes you 10 minutes to burn in the sun WITHOUT sunscreen, and you use an SPF 25, you can stay out in the sun 250 minutes. It is not cumulative, however. You can't re-apply after that 250 minutes of continuous sun exposure and expect the same results. SO...it sounds as if an SPF 25 is fine, but you will need to re-apply after work, before you go home again. The hot and smoky will sweat the SPF off. Let me know if you have any questions.