Black hairy tongue is caused by an overgrowth of dead skin cells, causing lengthening of the papillae, and staining from bacteria, yeast, food, tobacco or other substances in the mouth. Mayo Clinic does not endorse companies or products.
hairy tongue picture Black
Neville, Douglas D. Black hairy tongue is a condition of the tongue in which the small bumps on the tongue elongate with black or brown discoloration, giving a black and hairy appearance. Transient, surface discoloration that is not associated with hairy tongue can be brushed off. Gently brush the tongue with a toothbrush twice daily. Periodontium gingiva , periodontal ligament , cementum , alveolus — Gums and tooth-supporting structures.
Oral and maxillofacial pathology K00—K06, K11—K14 , —, — Causes include smoking or betel chewing ,  some foods and beverages e.