An omphalolith, also known as a umbolith, omphalith,[1] navel stone,[2] or umbilical concretion[3] is a periumbilical mass that may form due to the accumulation of sebum and keratin.[4] The colour is black or brown, and may be related to the skin type of the patient.[2] It may resemble a malignant melanoma.[5][page needed] It may be caused by poor hygiene,[6]: 121 and may form in retracted navels in obese people.[3]
The name was derived from the Greek words omphalos (Greek: ομφαλός), meaning navel, and lithos (Greek: λίθος), meaning stone.[3]