Hairs and swellings left and right in different places (8)
I believe the answer is:
Here is my best explanation:
'hairs' is the definition.
(bristle is a kind of hair)
I cannot understand how the remainder of the clue works.
(Other definitions for bristles that I've seen before include "Blisters with short stiff hairs", "Stiff hairs" and "Short stiff hairs".)