Hiding beard shadow requires the use of concealer and color corrector with a special technique.
Beard shadow is more than just a darker area it usually appears with a blueish or greenish hue based on skin undertone. You need to use a complementary color corrector with a tone which can neutralize the hue of the beard shadow. Then apply concealer on top of that in repeating layers to achieve a more uniform look.
After this you can still use foundation and rest of your makeup as you normally would.
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