What is a common complication of primary syphilis?

The formation of a chancre is a hallmark characteristic of primary syphilis. This stage of syphilis typically begins with the appearance of a single sore or ulcer known as a chancre at the site of infection, which may occur on the genitalia, anus, or mouth. The chancre is generally painless and can last for three to six weeks, healing spontaneously, but it is a definitive indicator of the primary stage of syphilis infection.

The other options listed focus on complications or conditions that do not specifically correlate with the primary stage of syphilis or arise from it. For example, impotence is a potential complication that may arise in advanced stages or due to other comorbidities and not directly from primary syphilis. Phimosis, the condition where the foreskin cannot be easily retracted, and cryptorchidism, a condition of undescended testicles, are unrelated to syphilis and are not complications that arise from its primary stage. Hence, chancre formation stands out as the most relevant and direct complication of primary syphilis, confirming the accuracy of the answer.