A pink patch on the scalp may be a birthmark, or it may be caused by scalp psoriasis, seborrheic dermatitis, lichen planus and other causes. 1. Birthmark: pink on the scalp if there are no other symptoms, just local scalp redness, and parallel to the skin, may be birthmarks such as bright red nevus, hemangioma and so on. 2. Scalp psoriasis: scalp psoriasis is a chronic inflammatory disease, and some patients with psoriasis will have scalp involvement. Skin lesions are manifested as discrete scaly plaques on the scalp and on the hairline, which usually extends to the forehead and the sides of the scalp. The plaques are pink and covered with silvery scales, which are sometimes bumpy to the touch and often itchy. 3. Seborrheic dermatitis: The scalp is a common site for seborrheic dermatitis, a long-term inflammatory skin condition that often harbors Malassezia bacteria. Light red patches or plaques appear on the scalp, usually accompanied by pimples and increased dandruff. 4. lichen planus: an inflammatory skin condition that can lead to bald patches on the scalp. It begins with reddish-purple patches on the scalp and may expand with hair loss. Afterward, the affected skin is left scarred and bald, most often with itching. If the birthmark is excluded, the patient can go to the hospital for a detailed examination to clarify the cause of the disease.