You can use layer masks to darken/lighten areas of an image.

For example: To darken selected parts of an image (correct for hot spots) create a new curves adjustment layer.

1) Darken the lightest point by moving the upper right hand point of the curve down.

2) Then darken the overall image slightly by moving the center point of the line down a little.

3) Switch the Black/white section to get white on top.

4) “Fill the image with black” by hitting Control + Backspace - this blocks the effect by filling with black

5) Set opacity to 50% and select a white brush

6) Now paint in white to paint the effect back into the image (paint over the hot spots to paint in the darken effect).

You can merge the layers into one layer, but continue to preserve the individual layers.

Shift + Control + Alt + N creates new layer

Shift + Control + Alt + E combines the existing layer into the new layer.