Indolent Ulcer in Cats

An indolent ulcer is a persistent sore that forms on the upper lip of cats, typically starting as a small reddish area that gradually develops into an open, well-defined lesion with raised edges. The term "indolent" reflects the way these ulcers behave—they tend to grow slowly and often seem painless, though the underlying tissue is inflamed and the surface does not heal in the usual way. The cause involves an abnormal immune response in the skin, though the exact trigger in an individual cat is not always clear. Owners often notice a thickened or eroded patch on one side of the upper lip, sometimes with a glistening or raw appearance. The cat may not seem particularly bothered by it, and there may be no obvious change in eating or grooming. The lesion can remain stable for weeks or months, or it may gradually enlarge if left unaddressed. This page explores the signs that may suggest an indolent ulcer, what is understood about the underlying process in the lip tissue, how the condition is typically investigated, and the range of approaches that exist for managing it. The focus is on helping you understand what may be happening and what shape a conversation with your veterinary team might take.