Hypersensitivity vasculitis is seen most commonly in -
Pathology hypersensitivity vasculitis 

In hypersensitivity vasuculitis, postcapillary venules are the most commonly involved vessels, capillaries and arterioles are involved less frequently.
It is primarily a disease of small vessels.
It is characterized by leukocytoclasis, a term that refers to the nuclear debris remaining from the neutrophils that have infiltrated in and around the vessels during the acute stages.
Post capillary venules
Arterioles
Veins
Capillaries