I always remember a lecture I heard a few years ago which suggested that “food” is best eaten and should not be put in moisturisers and this principle was reiterated at a recent lecture on atopic dermatitis I attended, exploring the link between atopic dermatitis and food allergy.
Around the world, a lot of natural food oils have been shown to have beneficial effects to improving the skin barrier function and moisturisation [1].
Atopic dermatitis is a very common inflammatory skin condition which can develop in infancy leading to flares and itching. The use of use of natural oils by some maybe sought as an alternative to medical prescriptions such as topical steroids due to fears around the unwanted side effects or steroid phobia which I have discussed in an earlier blog post.
A review published in 2019 [2] looked at published works investigating the use of natural oils for moisturisation – olive, sunflower seed and coconut oils. The conclusion was that no specific recommendation can be made on any one of them, but the authors point out that patients should be cautioned about potential negative effects, particularly for olive oil.
What’s the problem with Olive Oil?
Looking back through the literature, I found a paper from 1997 published in Contact Dermatitis [3]. The paper discusses how the oil is sometimes used as a moisturiser in skin care because of few reports of it causing any skin reactions, however, the authors suggest this may not be the case in patients with pre-existing skin disease. In the study 100 patients were patch tested with olive oil. Five patients showed a positive reaction. After examination of the patients and results they concluded that it was likely that olive oil was a weak irritant rather than an allergen and based on the profile of their patients it should be avoided on patients with impaired skin barrier such as eczema.
Effects of olive oil on skin barrier function
A later study in 2012, A UK research team in Sheffield [4] evaluated the effects of topical olive oil on the forearms of 19 patients (with and without a history of atopic dermatitis). Each volunteer applied six drops of olive oil to the forearm twice daily for five weeks in group one, and in the second group to apply the same, whilst applying six drops of sunflower seed oil to the other arm.
The normal lab measures of hydration, erythema, pH and trans-epidermal water loss from patients to determine the effects. They concluded that olive oil caused a significant reduction in the stratum corneum integrity and thickness, did not make any significant improvement in skin hydration and in some induced mild erythema (in both those with and without a history of atopic dermatitis). In contrast, sunflower seed oil improved skin hydration with no erythema or negative effects on the skin.
What is harmful to the skin in olive oil?
The reason for olive oil causing these issues probably relates to its composition. Olive oil typically has a high oleic acid (OA) to linoleic acid (LA) ratio. Previous work showed that skin irritancy is reduced when the ration is reversed (high LA to low OA) such as in sunflower seed oil. Oleic acid is a well-known penetration enhancer [5]. It does this by inserting itself into the skin surface lipids and disrupting the natural fat layers leading to increased water loss [6]. In addition, it is known to reduce skin integrity by its action on keratinocyte surface receptors.
Conclusion
From the work to date, it indicates that the chemical constitution of olive oil may mean it should not be recommended for regular emollient use - particularly for those with skin conditions. Of course, olive oil is one of many “natural” food derived oils that are used in skin care at varying concentrations and they are not all the same. As shown above sunflower seed oil, due to its chemistry had no harmful effects on the skin. More research into individual oils is required to ascertain their true potential benefits as moisturising agents.
References
1. Melguizo-Rodríguez L, González-Acedo A, Illescas-Montes R, García-Recio E, Ramos-Torrecillas J, Costela-Ruiz VJ, García-Martínez O: Biological effects of the olive tree and its derivatives on the skin. Food & Function 2022, 13:11410-11424. http://dx.doi.org/10.1039/D2FO01945K
2. Karagounis TK, Gittler JK, Rotemberg V, Morel KD: Use of “natural” oils for moisturization: Review of olive, coconut, and sunflower seed oil. Pediatr Dermatol 2019, 36:9-15. https://www.onlinelibrary.wiley.com/doi/abs/10.1111/pde.13621
3. Kränke B, Komericki P, Aberer W: Olive oil – contact sensitizer or irritant? Contact Dermatitis 2006, 36:5-10. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0536.1997.tb00914.x
4. Danby SG, AlEnezi T, Sultan A, Lavender T, Chittock J, Brown K, Cork MJ: Effect of Olive and Sunflower Seed Oil on the Adult Skin Barrier: Implications for Neonatal Skin Care. Pediatr Dermatol 2013, 30:42-50. https://doi.org/10.1111/j.1525-1470.2012.01865.x
5. Viljoen JM, Cowley A, du Preez J, Gerber M, du Plessis J: Penetration enhancing effects of selected natural oils utilized in topical dosage forms. Drug Dev Ind Pharm 2015, 41:2045-2054. https://doi.org/10.3109/03639045.2015.1047847
6. Jiang SJ, Zhou XJ: Examination of the mechanism of oleic acid-induced percutaneous penetration enhancement: an ultrastructural study. Biol Pharm Bull 2003, 26:66-68. https://www.jstage.jst.go.jp/article/bpb/26/1/26_1_66/_article