There are many causes of small red bumps on the penis, such as folliculitis, genital herpes, warts, syphilis rash and so on. 1. Folliculitis: secondary bacterial infection of the penile skin follicles may lead to the symptom of small red bumps on the penis. 2. genital herpes: herpes simplex virus infection caused by genital herpes, can also cause a small red bumps on the penis, with the progress of the disease will also appear blisters, ulcers and other symptoms. 3. warts: human papilloma virus infection caused by sexually transmitted diseases, can also cause a small red bumps on the penis, some will cause cauliflower-like, papillomatous organisms. 4. Syphilis rash: a sexually transmitted disease caused by syphilis spirochete infection, syphilis rash caused by second-stage syphilis, may also cause a small red bump on the penis. A small red bump on the penis, there may be other reasons, you need to go to the hospital in time to check, follow the doctor’s instructions for treatment.