Those who use sun block, a very wise thing to do, should not neglect their ears, behind their ears especially and necks, particularly if often engaged in north south flight routes, sun to one side and so to the other.
One side, smoothed with factor 50, depending upon route and seat will suffice to ward off a malignant melanoma. There is no real cure for metastasised melanoma cancer only surgical intervention and the plastic surgeon can only dig so deep into the body.