Swelling of the scalp may be caused by head trauma, cellulitis, contact dermatitis and other causes. 1. Head trauma: when the head is traumatized, it is easy to lead to scalp soft tissue congestion, edema, and thus the symptoms of scalp swelling. 2. Cellulitis: an acute infectious disease caused by bacterial infection secondary to trauma to the scalp, which can also cause redness and swelling of the scalp, tenderness and other symptoms. 3. Contact dermatitis: if recently replaced the new conditioner, shampoo or hair coloring, etc., may occur allergic reaction, so that the scalp edema erythema as well as corn size blisters, pimples, etc., accompanied by intense itching symptoms, the symptoms of severe cases will appear in the scalp area of the diffuse swelling. Scalp swelling may also have other causes, it is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease to give targeted treatment.