(scalp LP). Causes Cutaneous LP is a self-limiting condition. It usually resolves within 6 to 12 months. Oral LP is a non infectious, chronic inflammatory condition that involves the oral mucosa and may be accompanied by skin lesions. The etiology of oral LP are unknown. It is not clear whether the mechanisms causing isolated oral LP are different from those causing oral LP with cutaneous LP. An immune-mediated mechanism where basal keratinocytes are being targeted as foreign antigens by activated T cells, especially CD8+ T cells, has been proposed. Upregulation of intercellular adhesion molecule-1 (ICAM-1) and cytokines associated with T-helper 1 immune response, may also play an important role in the pathogenesis of lichen planus. Stress is thought to play a role in the pathogenesis of oral LP. Patients with anxiety and depression are reported more commonly with oral LP if compared to normal healthy individuals. Some studies have indicated that stressful events can induce LP lesions in otherwise healthy individuals. However, a cause effect relationship between stress and the onset of oral LP has not been demonstrated. Autoimmune response to epithelial self-antigens remains a possibility. A single study of cutaneous LP reported evidence in support of autoimmunity by expanding in vitro T cells isolated from the skin lesions of two patients, followed by testing the ability of these T cells to kill autologous keratinocytes (cytotoxicity). Several potential triggers of oral LP have been proposed over the years, mainly Hypersensitivity reaction Restorative material (e.g. amalgam and composite) or drugs can cause hypersensitivity reaction and lead to oral LP. Oral LP usually resolve upon removal of the trigger, as is characteristics of oral LP Viral infection Pathogenesis Oral LP is considered to be a T-cell mediated chronic inflammatory tissue reaction that results in a cytotoxic reaction against epithelial basal cells. The inflammatory infiltrate in oral LP is primarily composed of CD8+ T cells. A potential pathway for CD8+ T cell-mediated cytotoxicity in oral LP is described as follows: Antigens presented on MHC 1 molecules activates CD8+ T cells on keratinocytes or by encounters with activated CD4+ helper T cells or cytokines produced by activated CD4+ helper T cells Activated CD8+ T cells induce keratinocyte apoptosis through various mechanisms such as secretion of tumor necrosis factor (TNF)-alpha, secretion of granzyme B, or Fas-Fas ligand interactions. Chemokines are produced by activated CD8+ T cells that attract additional inflammatory cells, thereby promoting continued inflammation.