One of the main causes of sinus drainage is simply being alive. Every day the human body produces several liters of sinus fluid and mucus, and all of that natural liquid must go somewhere.
It is a area of tenderness of the scalp in which people also sometimes feel stabbing headaches. Others just feel very sore and tender to the touch. It is felt to be caused by irritation of the connective tissue which attaches the muscles of the scalp to the skull (cranium).
Mild seborrheic dermatitis that affects the scalp is called dandruff (pityriasis sicca) and results in a characteristic flaking. Of note, in infants, mild seborrheic dermatitis results in a condition called cradle cap.. Dandruff can begin in childhood and has a gradual onset.