The effects of UV on the skin mainly include acute inflammation (erythema/edema) and abnormal keratinization wherein prostaglandin E<sub>2</sub> (produced by cyclooxygenase-2), interleukin-8 and transglutaminase 1 (a major regulatory factor of keratinization) play pivotal roles.
Cyclooxygenase-2 (COX-2) is a membrane-associated enzyme that produces prostaglandin E<sub>2</sub> (PGE<sub>2</sub>) at sites of pulpal injury and inflammation, which leads to tissue swelling, redness and pain.
Axon reflex erythema upon mechanical and thermal stimuli was significantly increased 3 h after irradiation and particularly strong at 6 h. A significant modulation of 9 genes was found post UV-C irradiation, including NGF (3, 6, 24 h), TrkA (6, 24 h), artemin, bradykinin-1 receptor, COX-2, CCL-2 and CCL-3 (3 and 6 h each).
Luteolin also inhibited both UVB-induced skin erythema and the upregulation of cyclooxygenase-2 and prostaglandin E₂ production in human skin via interference with the MAPK pathway.