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).
In fact, some barrettes, hair combs, and even hats can cause or contribute to the development of a tender scalp. In some cases, a person may actually cause herself to have scalp tenderness. For example, some people are overly rough when it comes to grooming themselves.