Over 18 months, your Braun shaving cassette cuts over 6,000,000 hairs cut over 6,000,000 hairs. Over time, the cutting parts naturally start to wear down. We therefore recommend replacing the shaver head every 18 months, to keep your shave to a few strokes and reset your electric shaver to new. By routinely replacing the shaver head, your shaver body will remain in peak condition for years to come.