There are many reasons for the appearance of a lump behind the head. Although generally not dangerous, you should be vigilant when the lump is accompanied by headaches, vomiting, bleeding, or if the size continues to grow. Lumps behind the head can vary from size, color, and shape. There are soft, hard, itchy, disturbing appearance, or no pain at all. A dangerous lump behind the head that is accompanied by pain and prolonged headaches despite taking painkillers. Causes of Lumps Behind the Head Some causes of the appearance of a bump behind the head are: Collision or accident Lumps can appear when the head collides with a hard object or a head injury occurs. This is the body's reaction to self-healing. Lumps on the back of the head can cause bruising or hematoma on the scalp. Purplish-colored bumps are a sign that you are experiencing bleeding under the skin. Strong collisions can indeed cause large lumps and even bleeding in the brain, but generally the lump will di...