I know that with foreskin you are prone to this, the whole reason behind circumcision. With foreskin you must take extra care, pull it back while urinating and dab your penis with soft tissue, dont shake it all over. In your daily shower, pull it back and gently wash with a mild soap, no chemicals or perfumes. Also dab dry, pull it back 10 minutes later and make sure its dry, pull it back often to get air too when you can.
Use Vitamin E if you masterbate, its great for your skin. If it spreads, get to a doctor.