White substance inside foreskin

No need to worry. Yes, it's normal providing it washes fairly easily off. It's called smegma and you should clean it off- pull your foreskin back as far as it goes and gently wash it clean with slightly soapy water (not too much soap). It's normal, but you need to keep it clean to keep your penis healthy. Hope that helped dude

You may not be rinsing properly.
Try having showers instead of baths, your bathing in dirty
water.
Make sure you soap up and rinse off with plenty of water
after wards and also dry properly.