Hair can be a countable noun or an uncountable noun.
used as a countable noun
Each of the thread-like things growing on your head and body is a hair. You can refer to several of these things as hairs.
These tiny needles are far thinner than a human hair.
There were black hairs on the back of his hands.
used as an uncountable noun
However, don't refer to all the hairs on your head as your ‘hairs’. Refer to them as your hair.
I washed my hands and combed my hair.
Brigitte was a young woman with long blonde hair.