Background: Potash alum mouth rinse has been well studied with appreciable success in protection against carious lesions and periodontal microbiota with no adverse reactions. While oral lichenoid reactions have been documented as complications of various dental materials and drugs none has been reported as a result of alum use. Case Description: An unusual oral lichenoid reaction to potash alum use in an adult patient who presented at the oral medicine and diagnosis clinic of the dental centre of the Lagos State University Teaching Hospital. He presented with complaints of excessive salivary flow and dark pigmentation of the palate, and a history of potash alum licking for more than a month. On examination a dark pigmentation involving the palatal gingiva related to 24-27, sialometry revealed normal salivary flow Hence a diagnosis of false sialorrhoea was made. The patient was referred to the Periodontology unit of the same institution where an excisional biopsy was carried out, this was diagnosed as a lichenoid reaction by the Oral Pathology unit. The patient was counselled to stop the use of alum and reassured about the normal salivary flow. The patient reported tremendous improvement on review. Conclusion: Many home remedy habits and practices can be harmful, this underscores the role of counseling patients against these unverified remedies.