<p>Acitretin is a retinoid, an aromatic analogue of vitamin A. The mechanism of action of acitretin is unknown, however, evidence exists for a wide range of actions at various cellular and subcellular levels. These include regulation of RNA/DNA synthesis, modulation of factors which influence epidermal proliferation, modification of glycoprotein synthesis and modulation of the immune response. Whatever the exact mechanism of action, the most prominent effect of acitretin is a modulation of cellular differentiation in the epidermis which re-establishes a more normal pattern of cell growth.</p>