The filiform papillae on the dorsum (top) surface of the tongue are a bit like hair in that they keep growing throughout your life. The image above is actually an electron micrograph of a cat’s tongue. Most people are familiar with the way a cat’s tongue feels when they are licked by one. This EM shows why they feel so scratchy. Human filiform papillae are much more boring. They are flatter and tend to lie down like the ones beside the larger fungiform papilla in the micrograph below.
In healthy people, the individual hairs are shed before they get too long, and the natural red color of the underlying tongue tissue shows through giving the velvet a pink appearance.
In some disease conditions (mostly fever causing diseases), the hair does not shed easily and forms a white, or sometimes even a black “coat” on the dorsal surface of the tongue. The filiform papillae are naturally white, but are often stained brown or black by foods or by dry mouth. When the filiform papillae grow too long, they remain on the dorsum of the tongue like a thick mat. This condition is known as “white hairy tongue” or “black hairy tongue” (see images below).
A white or black coating on the tongue is NOT necessarily associated with any particular disease condition. This overgrowth of “hair” is easily removed by scraping the surface of the tongue with a tongue scraper. The filiform papillae are not associated with the sense of taste. White and black hairy tongue are not contagious conditions. Click on either image below to see larger versions. The filiform papillae, especially on the back of the tongue, are heavily implicated in the production of bad mouth odors. See my page on halitosis for more on that subject.