Stink Shrink is first mentioned in Everblaze (pg. 269 paperback), and is said to work similarly to deoderant. It was only mentioned once when Sophie was preparing for Fintan's healing. It is assumed that Sophie was using this to smell acceptable for the healing where all of the Councillors, Tiergan, Alden, and Fitz would be, as she was wearing multiple layers of clothes that caused her to sweat. It is presumably sold at Slurps and Burps.