The fame of cats being extremely clean animals is widely known. They posses different anatomical characteristics which help them in their grooming process constantly:
1. An impressive flexibility which allows it to reach any point of its body with its tongue.
2. A coarse tongue to clean itself with.
3. Both its teeth and claws help in this process as well.
Cleaning (commonly known as Grooming in cats) has other functions besides personal hygiene. It reactivates/stimulates blood flow and it tones their muscles.
It is also a character reflex; in some cases when they are nervous and in other when they are bored. They learn this from their mother when they are 1 month old.
In some cases, cats don't develop this form of stimuli. The burden falls upon us to care for their fur/hair. In the case of cats which live in a group (litter), they groom each other.