hello thanks for consulting at hcm.hairy appearance is due to the elongation of keratinized filiform papillae, which may have different colors varying from white, yellow, brown, to black depending upon the involved extrinsic factors (ie, tobacco, coffee, tea, or food) and intrinsic factors (ie, chromogenic organisms in the normal flora).main source of the pigments -a local reaction between the decomposition products of food and iron (secondary to blood within the mouth).. other Factors associated- include drugs such as antibiotics (penicillin, cephalosporin, chloramphenicol, streptomycin, and tetracycline),corticosteroids, oxygenating mouth rinses, nonsteroidal anti-inflammatory drugs and psychotropics, as well as tobacco, vegetable dyes, radiation, poor oral hygiene. kindly check with ur physician if prblm persists..u have to rule most causative factor such as mouth wash or any drug which u r using,,also plz chck with ur oral medicine specialist also,,hope it helps,,tc