Circumcision is impossible without leaving a scar. Fortunately in many men it leaves a flat scar that does not interfere with function. Sometimes the scar is raised or contracted. When this happens it may interfere with penile function, especially when they are sexually aroused and have an erection. For some men this can be painful or cause the penis to be bent.
Male Genital Surgery
One study showed circumcised men had many "physical consequences of circumcision…the most common being scarring; there were small scars in 63% and large scars in 9% of the circumcised men"(Kim 2006). While uncommon, if cancer of the penis occurs in circumcised men it is often in the scar (Seyam 2006). It is usually a squamous cell carcinoma or so-called Marjolin’s ulcer
Scar revision on the penis after circumcision is difficult but in some cases it is possible. Unfortunately the shortage of skin created by removing the normal prepuce makes results unpredictable. Some men are already short of skin, especially when erect, and this can cause pain and discomfort. The only solution for them is the use of skin grafts or flaps.
References:
Kim, D., & Pang, M.-G. (2007). The effect of male circumcision on sexuality. BJU international, 99(3), 619–622. doi:10.1111/j.1464-410X.2006.06646.xdoi:10.1111/j.1464-410X.2006.06646.x
Seyam, R. M., Bissada, N. K., Mokhtar, A. A., Mourad, W. A., Aslam, M., Elkum, N., Kattan, S. A., et al. (2006). Outcome of Penile Cancer in Circumcised Men. The Journal of urology, 175(2), 557–561. doi:10.1016/S0022-5347(05)00234-X