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).
Though you may not be able to see bumps on your scalp due to the thickness of your hair, you may first feel the irregularities with your fingertips during shampooing, styling your hair or scratching your scalp. Various conditions can cause bumps to appear on and under the surface of your scalp skin.