The tiny white crescents or blisters that can appear just under the surface of polymer clay are called Moonies. To help reduce the appearance of Moonies you can choose flesh colored polymer clay, one that is less translucent and is lighter colored, or whiter, (usually more opaque) and those properties make Moonies much less obvious.
What causes Moonies?
One theory is over-smoothing the clay. Another theory is trapped air under the surface.
By pulling and stretching clay in one direction, you may be making little stress tears under the surface. If you smooth carefully, patting the clay and pulling in different directions, then patting again, you can smooth the surface without causing underlying stresses. If you see a Moonie before you bake your sculpt, you can try making a pinhole into the Moonie and gently pressing out the trapped air.
This doll maker demonstrates how she repairs a Moonie: