What Causes the Lack of Hair on the Back Half of a Child’s Head?

Question

What causes the lack of hair on the back half of a child’s head?

Answer

The child is four months old, and after being shaved on the first full month, hair has grown on the front half of the head but not on the back. The doctor advises appropriate calcium supplementation, sun exposure, and keeping warm. Furthermore, it’s important to avoid catching a cold and to wish for a happy life.