The shaver heads of your Philips electric shaver shave millions of hairs in 1 year. This causes inevitable wear and tear on the blades, so you can no longer get a smooth shave after some time. In addition, a lot of grease and dirt sticks to the shaving head after multiple shaves, which causes razor burn and acne. You can prevent this if you replace the shaver head after about 2 years. Make sure you check the type numbers, so you know for sure that the shaver head is suitable for your shaver.