How can I lighten shadowed skin areas in Photoshop using masks and adjustment layers?

Yes—Photoshop can target only the shadowed areas by using a selection plus an adjustment layer. Select the area you want to correct (for example with the Lasso, Magic Wand, or another selection tool), then add an adjustment layer. Photoshop will automatically turn that selection into the adjustment layer’s mask, including any feathering.

For this kind of correction, use a subtle Levels adjustment (or similar brightness/tone adjustment) to lift the darker skin areas until they better match the surrounding tones. Because the correction is on a mask, you can refine it afterward by painting or editing the mask like any other layer mask. You can also copy and paste masks between layers if needed.

So while there isn’t a one-click “remove all shadows” solution described here, a masked adjustment layer is the standard way to even out localized shadows non-destructively.