Common causes of a small pustule on the penis include folliculitis, warts and syphilis. 1. Folliculitis: If the location of the small pustule is on the penis and the pustule is not painful or itchy, there may be a follicular infection, which can be applied by topical ointment, such as erythromycin ointment. 2. Condyloma acuminatum: if the location of the small pustules in the inner plate of the foreskin or around the glans, and the shape of the cauliflower pattern, considered to be the symptoms caused by condyloma acuminatum, you can be given physical therapy, such as laser, cold therapy, and so on. 3. Syphilis: If the small pustules are located on the glans and accompanied by ulceration, you need to consider the possibility of syphilis. Regardless of which of the above causes of penile pustules, if the time persists longer, it is recommended to go to the hospital in time for diagnosis, early detection and timely treatment.