Why won't my face tan?

Whenever I sit outside for a few hours, my body gets really tanned, but my face doesn't. For comparison, I ride my bike every day and my face is always exposed. My arms aren't always, because sometimes I have to wear a a jacket. And yet, my arms are much darker than my face. What could be causing that and does anyone else have this?
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+1 y
I never wear foundation or any powders, so that can't be it.
Why won't my face tan?
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