Key Clinical MessageOral chemical ulceration is a rare condition. The causes differ from misuse of dental material by dentists and over‐the‐counter drugs (OTC) to the herbal ingredients in our foods. Detailed patient history helps to explore the diagnosis and further management of such a lesion, which extend from no intervention in mild cases to surgical intervention in severe cases. This report represents a case of chemical ulceration of the mouth caused by hydraulic fluid oil leakage inside a dental chair in a 24‐year‐old female, leading to the patient developing multiple painful oral ulceration after surgical extraction. The purpose of the report is to increase awareness among health practitioners of unusual causes that could happen during dental interventions.