12-Hydroxyeicosatetraenoic acid (12-HETE) is an eicosanoid. It is a metabolite of arachidonic acid produced by the action of the enzyme arachidonate 12-lipoxygenase. 12-HETE is a highly selective ligand used to label mu opioid receptors. 12-HETE can activate Cdc42, Rac1 and PI-3K, which then participate as upstream signalling molecules for PAK1 and JNK1 activation. 12-Hydroxyeicosatetraenoic acid (12-HETE) is a chemotactic stimulus for epidermal cells. 12-hydroxyeicosatetraenoic acid (12-HETE), the main eicosanoid in skin, is assumed to have both pathophysiologic effects in inflammatory skin diseases such as psoriasis and atopic eczema and a physiologic role in the biology of cutaneous reparative processes. The modulation of epidermal 12-HETE receptors by UV-B may partly explain the therapeutic effects of UV-B, but possibly also contribute to photodamage to skin.