Dietary omega-3 polyunsaturated fatty acids (omega-3 PUFA) reduce sunburn, an acute inflammatory response, in humans. We assessed whether this may be mediated by reduced ultraviolet-B (UV-B) induction of proinflammatory mediators tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta, IL-6, IL-8 and prostaglandin (PG)E(2) in healthy skin. In a double-blind, randomized study, 28 humans received 4 g daily of 95% ethyl esters of eicosapentaenoic acid (EPA) or oleic acid (OA) orally for 3 months. Skin biopsies and suction blister fluid were taken from unexposed and UV-B-exposed skin and examined for mediator expression immunohistochemically and quantitatively by immunoassay; plasma levels were also assayed. The subjects taking EPA, but not OA, showed a significant rise in their minimal erythemal dose (MED) (data reported elsewhere). Before supplementation, irradiation with 3x MED UV-B increased blister fluid TNF-alpha, IL-6, IL-8 and PGE(2) at 16 h (all P < 0.001). No significant change occurred in baseline or UV-B-induced skin levels of cytokines after either supplement, whereas UV-B induction of PGE(2) was abolished after EPA but not OA. Immunohistochemical expression of the cytokines at baseline and after UV-B was unaltered by EPA and OA; circulating cytokine and PGE(2) levels were also unchanged. Hence, in healthy skin in vivo, there was no evidence that reduction of the sunburn response by EPA is mediated by the proinflammatory cytokines examined; abrogation of UV-B-generated PGE(2) may play a role.