Why are black rings formed around mouth?

Black rings around the mouth can be caused by several factors, including hyperpigmentation, which may result from excessive sun exposure, hormonal changes, or certain medications. They can also be related to skin conditions like melasma or contact dermatitis due to irritants. Additionally, poor oral hygiene or smoking can contribute to discoloration in the area. If the rings persist or are accompanied by other symptoms, it's advisable to consult a healthcare professional for an accurate diagnosis and treatment.