Cosmetic application of Marula seed oil (Sclerocarya birrea): Clinical outcomes

Marula oil, extracted from the kernels of Sclerocarya birrea (Anacardiaceae), is traditionally used by southern African women as a moisturising agent on their faces, feet and hands. The seed oil is rich in mono-unsaturated fatty acids that have hydrating and moisturising properties. The oil is a popular ingredient in cosmetics such as skin lotions, lipsticks and foundations. The demand for marula oil produced by rural communities in Namibia has increased tremendously such that in 2008 almost US$ 20 million was spent on the oil for cosmetic products by The BodyShop® and Aldivia®. Despite its popularity, scientific evidence for efficacy and safety to support the traditional as well as cosmetic use is still lacking. This study evaluated the irritancy potential (safety), moisturising and hydrating effects as well as occlusivity properties (efficacy) of marula oil upon topical application. In addition, the oil composition was determined using two-dimensional gas chromatography. Healthy Caucasian adult female volunteers (n = 20) who complied with the inclusion and exclusion criteria for the irritancy patch and moisture efficacy tests participated in the study. A 2x magnifying lamp (Visual observation), Chromameter®, Aquaflux® and Corneometer® were used to evaluate and monitor the irritancy level, skin barrier function, trans-epidermal water loss, hydrating and occlusive effects, respectively. The results revealed that marula oil is non-irritating (p < 0.001), with hydrating properties (p < 0.001) when applied to a lipid-dry (xerosis) skin and moisturising (p < 0.001) when applied to normal skin. These findings may be linked to the easy absorption of the oil into the skin due to the high percentage of oleic acid (69%) followed by palmitic acid (15.3%), linoleic acid (9.2%), palmitoleic acid (4.1%) and stearic acid (1.5%). The study provides scientific basis for inclusion of marula oil in cosmetic formulations as it is non-irritating and provides moisturising effects with moderate prevention of trans-epidermal water loss which may alleviate premature-aging.