Razors with multi blade systems have replaceable blades that you can easily detach and attach a new fresh blade to. As soon as you feel the sharpness of your blades start to decline you should consider changing it. Shaving with a dull blade brings no pleasant experience and the result is no good. Make sure you always have extra multi razor blades at home and buy the blades that fit your razor. Here you can find razor blades that fits to both Gillette and Lea razors.