There are many reasons why the surface of the glans is as black as a turtle shell, such as physiological phenomenon, external stimulation, glansitis, allergies and other reasons. 1. Physiological phenomenon: the glans will be congested when the penis is erected, and the obstruction of venous return will cause the glans to be crimson in color, purplish-red, and even blackened like a tortoise shell, which is generally normal and does not require treatment. 2. external stimulation: for example, the glans is extruded by external forces, or excessive masturbation, frequent sexual intercourse, can also cause congestion and swelling or subcutaneous capillary rupture, resulting in the surface of the glans as black as the turtle shell. 3. glansitis: external pathogenic bacterial infection causes inflammatory reaction of the glans, which can also cause swelling of the glans, and there is a possibility that the surface of the glans is as brittle as the turtle shell. 4. Allergy: for example, contact dermatitis of the mucous membrane of the glans skin, eczema and other reasons, can also cause the surface of the glans to be black like a tortoise shell, and most of them will also be accompanied by itching and rashes. The surface of the glans is as black as a turtle shell, there may be other reasons, you need to go to the hospital in time to check, follow the doctor’s instructions for treatment.