The pink stuff on your shower head is a type of mold that is caused by the growth of an airborne bacterium called Serratia marcescens.
The pink mold can also be inside your shower as well so you want to clean your shower often with some vinegar or other disinfectant.
Scrubbing the shower down with some bleach can also kill the bacteria that causes the pink mold in the shower and on the shower head.
You can get rid of the pink mold on the shower head by diluting some bleach and soaking the shower head in some diluted bleach.
The bleach will kill the bacteria that is causing the pink mold on the shower head.
You can soak the shower head in a bag diluted bleach or remove the shower head and soak it in a bucket of diluted bleach.
Also soaking the shower head in vinegar can also help get rid of the pink mold on the shower head.