A black tongue is usually caused by a buildup of dead skin cells (keratin) on the tiny bumps on the tongue called papillae, which can trap bacteria, fungi, food, and other substances that stain the tongue. This condition is known as black hairy tongue and although it can look alarming, it is typically harmless and temporary. Factors contributing to this condition include poor oral hygiene, smoking, drinking coffee or tea, use of antibiotics, dry mouth, certain medications (such as those containing bismuth), eating a soft diet, use of harsh mouthwashes, and radiation therapy to the head or neck. It may also cause symptoms like bad breath, a metallic taste, thick texture on the tongue, and a hairy appearance on the tongue's surface. Improving oral hygiene and addressing underlying causes usually clears the condition without complications.