Hairy leukoplakia is a white patch on the side of the tongue with a corrugated or hairy appearance. It is caused by Epstein-Barr virus (EBV) and occurs usually in persons who are immunocompromised, especially those with human immunodeficiency virus infection/acquired immunodeficiency syndrome (HIV/AIDS). The white lesion, which cannot be scraped off, is benign and does not require any treatment, although its appearance may have diagnostic and prognostic implications for the underlying condition. Depending upon what definition of leukoplakia is used, hairy leukoplakia is sometimes considered a subtype of leukoplakia, or a distinct diagnosis. Signs and symptoms There are no symptoms associated with the lesion itself, although many and varied symptoms and signs may be associated with the underlying cause of immunosuppression. The lesion is a white patch, which almost exclusively occurs on the lateral surfaces of the tongue, although rarely it may occur on the buccal mucosa, soft palate, pharynx or esophagus. The lesion may grow to involve the dorsal surface of the tongue. The texture is vertically corrugated ("hairy") or thickly furrowed and shaggy in appearance. Causes The white appearance is created by hyperkeratosis (overproduction of keratin) and epithelial hyperplasia. The causative agent implicated is Epstein-Barr virus, the same virus that causes infectious mononucleosis (glandular fever). After the primary EBV infection has been overcome, the virus will persist for the rest of the host's life and "hides" from the immune system by latent infection of B lymphocytes. The virus also causes lytic infection in the oropharynx, but is kept in check by a normal, functioning immune system. Uncontrolled lytic infection is manifested as oral hairy leukoplakia in immunocompromised hosts. OHL usually arises where the immunocompromise is secondary to HIV/AIDS. Rarely are other causes of immunocompromise associated with OHL, but it has been reported in people who have received transplants and are taking immunosuppressive medication. OHL may also accompany chronic graft versus host disease. Even more rare are reports of OHL in persons with competent immune systems. Diagnosis The white lesion cannot be wiped away, unlike some other common oral white lesions, e.g. pseudomembranous candidiasis, and this may aid in the diagnosis. Diagnosis of OHL is mainly clinical, but can be supported by proof of EBV in the lesion (achieved by in situ hybridization, polymerase chain reaction, immunohistochemistry, Southern blotting, or electron microscopy) and HIV serotesting. When clinical appearance alone is used to diagnose OHL, there is a false positive