In vitro and in vivo assessment of the effect of Laurus novocanariensis oil and essential oil in human skin.

Laurus novocanariensis is an endemic plant from the Madeira Island forest that derives a fatty oil, with a strong spicy odour, from its berries that has been used for centuries in traditional medicine to treat skin ailments. This work aimed to investigate the effect of the application of both the oil and its essential oil on normal skin, to assess their safety and potential benefits. Diffusion studies with Franz cells using human epidermal membranes were conducted. The steady-state fluxes of two model molecules through untreated skin were compared with those obtained after a 2-h pre-treatment with either the oil or the essential oil. Additionally, eleven volunteers participated in the in vivo study that was conducted on the forearm and involved daily application of the oil for 5 days. Measurements were performed every day in the treated site with bioengineering methods that measure erythema, irritation and loss of barrier function. Slightly higher steady-state fluxes were observed for both the lipophilic and the hydrophilic molecule when the epidermal membranes were pre-treated. Nevertheless, such differences had no statistical significance, which seems to confirm that neither the oil nor the essential oil impaired the epidermal barrier. Results collected with the Chromameter, the Laser Doppler Flowmeter and the visual scoring are in agreement with those established in the in vitro study. They indicate that the repeated application of the oil did not cause erythema, because the results observed in the first day of the study were maintained throughout the week. Application of the oil did not affect the skin barrier function, because the transepidermal water loss remained constant throughout the study. The stratum corneum hydration was slightly reduced on days 4 and 5. This work shows that both the oil and the essential oil were well tolerated by the skin and did not cause significant barrier impairment or irritation.