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).
Sometimes, however, a tender scalp may be caused by hair that is very heavy and pulls on the scalp. There are even some conditions, such as ringworm and acne, that contribute to a sore scalp. In some cases, a person may even develop a tender scalp because of overly energetic combing and brushing.