On first glance, it doesn't look like an artifact. It reminds me of the bands visible on 3d printed objects. There are similar lines behind the ear, but at a different angle (but those behind the ear look like brush marks). Does the artifact appear when repeat photos of the same figure are taken?
It could be a compression artifact. If you have the raw image file (.nef or .nrw for Nikon cameras), view it directly or convert it to an image format that uses lossless compression, like png. Then check the image to see if the artifact is still there.