Dry skin. Coloured scanning electron micrograph (SEM) of dry skin from the knuckles. While all skin is shed continuously, dry skin is shed at a higher rate, leading to a flaky appearance. Dry skin may be caused by a poor diet or exposure to irritants. It is also very common in the winter when low humidity leaves skin dry and itchy. Magnification: x650 when printed at 10 centimetres wide.