Small red bumps on the penis may be caused by allergic reactions, condyloma acuminatum, pearly penile papules and other factors. 1. Allergic reaction: If the material of the underwear is inferior, it may lead to an allergic reaction on the penis, resulting in the appearance of small red bumps, which, in this case, is usually accompanied by itchy skin. 2. Condyloma acuminatum: mainly caused by infection with the human papilloma virus, mainly manifested in the penis, scrotum, around the anus and other parts of the emergence of small reddish or skin-colored pimples, usually gradually increase, look dense. 3. Pearly penile papules: long foreskin and lack of attention to local hygiene may lead to pearly penile papules, resulting in pearly reddish papules at the junction of the glans penis and foreskin. It is recommended to wear cotton loose underwear, if there is a small red pimples on the penis, you should seek medical attention in time to avoid delay.