To some men, bicycles may look like the key to good health and a prosperous sex life—riding around all day keeps you fit and attractive; you can save that $4.50 a gallon of gas money for your date/girlfriend/boyfriend/house party; and you get to wear really, really tight clothes. But there's a downside. Cycling can also cause genital numbness, erection problems and skin irritations in the groin area, a new report in the urology journal BJU International confirms, citing several medical studies over the last few years.