Regularly sick, chafes in prison (6)
I believe the answer is:
scrubs
'prison' is the definition.
(Wormwood Scrubs)
'regularly sick chafes' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'chafes' becomes 'rubs' ('rub' can be a synonym of 'chafe').
The alternating letters of 'sick' are 'sc'.
'sc'+'rubs'='SCRUBS'
'in' is the link.
(Other definitions for scrubs that I've seen before include "special clothing for those working in the theatre" , "Wormwood _____" , "Clothing worn in an operating theatre" , "Abolishes" , "Protective garments for surgeons" .)