Pinhole-sized pimples on the skin of the penis may be associated with cornrows, penile herpes, and warts. 1. Corns: due to epithelial benign tumors or retention cysts of the epidermis or appendages of the skin, can occur on the penis. It manifests itself as a white or yellow needle-sized firm papule with a rounded tip. The hard white granular material can be extruded by picking out the papule. 2. Penile herpes: caused by herpes simplex virus infection, initially appearing in the penis localized red small papules, quickly turned into herpes, mostly patchy distribution. When the herpes breaks, an ulcer is formed and the base is red. 3. acromegaly: a sexually transmitted disease caused by sexual intercourse, often manifested in the skin and mucous membrane junction of soft superfluous organisms, such as male genitalia and perianal parts, initially for a single, scattered or dense reddish pinhead-like size of the papules, and gradually increased and fused into a piece. There are many other causes of pinhole-sized pimples on the penis skin, you should seek medical attention in a timely manner, with the help of a doctor to clarify the cause, targeted treatment or therapy.