Effects of hot water extract of Curcuma longa on human epidermal keratinocytes in vitro and skin conditions in healthy participants: A randomized, double-blind, placebo-controlled trial

Background: Curcuma longa has been reported to have anti-inflammatory effects. Skin inflammation impairs skin functions. Objectives: Our aim was to investigate the effect of a hot water extract of C longa (WEC) on skin conditions in cell studies using keratinocytes and in clinical trials. Methods: We measured proinflammatory cytokine levels in ultraviolet B-irradiated keratinocytes in the presence or absence of WEC. The effects of WEC on hyaluronan production in keratinocytes were also determined. In a randomized, double-blind, placebo-controlled trial, 47 healthy participants were assigned to 8-week intervention groups with daily intakes of WEC with or without curcumin or a placebo. The water content and transepidermal water loss in the face and minimal erythema dose on the back after ultraviolet B irradiation were evaluated every 4 weeks. Results: Hot water extract of C longa significantly inhibited increases in ultraviolet B-induced tumor necrosis factor alpha and interleukin 1 beta at the mRNA and protein levels. WEC also significantly increased hyaluronan production from nonstimulated keratinocytes. In the randomized, double-blind, placebo-controlled trial, increases from baseline in the water content of the face were significantly greater at weeks 4 and 8 in the WEC group, but not in the WEC + curcumin group, than in the placebo group. There were no significant differences in transepidermal water loss and minimal erythema dose among the groups. Conclusions: The cell studies confirmed that WEC has anti-inflammatory effects and augments hyaluronan production in the skin. The results of clinical trials suggest that WEC may be useful for moisturizing facial skin. Trial registration: UMIN Clinical Trials Registry 000028510. Retrospectively registered.