After about 1.5 years of shaving with your Braun shaver, it's time to to replace the entire shaving cartridge. With a new shaver head, you maintain your smooth shave and prevent skin irritation and acne. That's because a shaving foil is full of dirt, grease, and hair after those 1.5 years. This isn't hygienic and it can damage your skin. There's a different shaving cassette for each series, so check the type numbers carefully.