There are many reasons that a tooth becomes discoloured.  Extrinsic causes are something that comes in contact with the tooth.  Intrinsic causes are changes within the tooth.  Lastly, age-related changes can also change tooth colour. Some examples are: Foods/drinks. Coffee, tea, colas, wine, and certain foods and spices can stain teeth Tobacco use. Smoking or chewing tobacco can stain teeth Poor Oral Hygiene. Not brushing, flossing, and rinsing can cause discoloration Certain diseases can cause discoloration.  Treatment options. Such as radiation therapy or chemotherapy Certain antibiotics and medicated mouth rinses can cause staining Dental Materials. Different dental restorations are grey in appearance and can tarnish teeth As we age, enamel wears away and reveals the natural colour of dentin Some people have naturally darker or brighter enamel Certain people breath through their mouth can accumulate work-related dust Trauma.  Damage to teeth can change the colour of a tooth