Which Vegetable Oils Speed Up Skin Healing, and Which Slow It Down: New Study

Laboratory studies have revealed which plant oils speed up skin regeneration and which slow it down, as well as which combinations of fatty acids are behind these effects.

Scientists from the University of Ljubljana (Slovenia) investigated the effect of selected plant oils and their components on the growth and migration of skin cells. Their study, published in the journal Scientific Reports, confirms the role of plant oils in enhancing skin cell regeneration.

Prerequisites

The skin is the largest human organ and acts as a protective barrier against foreign agents such as pathogens, chemicals and radiation. Keratinocytes and fibroblasts are the main types of skin cells that play a key role in the restoration and regeneration of the skin during the inflammatory phase.

Plant oils used in therapeutic and cosmetic products have potential for healing damaged or traumatized skin. Triglycerides, which include saturated and unsaturated fatty acids, are the main components of plant oils (99%) and are known to have a wide range of beneficial effects, including antimicrobial, anti-inflammatory, antioxidant, and skin regenerating properties.

Vegetable oils also contain small amounts (~1%) of unsaponifiable compounds such as phytosterols, phenolic compounds, squalene, carotene and vitamins, which also have antimicrobial, antioxidant and anti-inflammatory properties.

There is evidence that microbial lipases in the skin hydrolyze triglycerides to release free fatty acids. Some of these acids, such as linoleic acid, are known to protect skin integrity, while others, such as oleic acid, have a destructive effect on the skin barrier.

The physiological ratio of oleic to linoleic acids in the outermost layer of the skin is 3:1. Any imbalance or deficiency in the skin's lipid profile can cause excessive dryness or oiliness of the skin and associated skin diseases. However, evidence regarding specific free fatty acid ratios that can predict whether a particular vegetable oil will have a positive or negative effect on skin cells is still lacking.

In the present study, the researchers examined the effects of selected plant oils and their components on the growth and migration of fibroblasts and keratinocytes, focusing on the fatty acid component of triglycerides and unsaponifiables.

Scientists cultured fibroblasts and keratinocytes in the laboratory and tested the effects of coconut, olive, linden, poppy, pomegranate, calendula and linseed oils on cell growth and wound healing (cell migration).

Key Results

The results of the study showed that most of the tested vegetable oils moderately but significantly increased the growth of fibroblasts and keratinocytes, with the exception of pomegranate seed oil and its main fatty acid (punicic acid), which significantly inhibited skin cell growth. Coconut and olive oils had no significant effect on skin cell growth.

Vegetable oils high in essential fatty acids, including linoleic and α-linolenic acid, had the most pronounced positive effects on cell growth. However, α-linolenic acid showed a biphasic effect, strongly inhibiting the proliferation of both keratinocytes and fibroblasts at higher concentrations (0.01 mg/100 μl) at both 48 and 72 hours, while a stimulatory effect was observed at lower concentrations (0.005 mg/100 μl) and at certain time points.

After 48 or 72 hours, most proliferative (growth enhancing) effects were observed at concentrations of oils such as poppy, linden, flax and calendula at 0.15% or 0.1%, while lower concentrations (0.01%) generally showed no significant activity.

The individual fatty acids in the vegetable oils had different effects, with some (lauric and myristic acids) stimulating skin cell growth and others (palmitic acid) consistently inhibiting the growth of both fibroblasts and keratinocytes at all concentrations tested at both 48 and 72 hours. Given the importance of the oleic to linoleic acid ratio in skin health and disease, the study assessed the effects of three different ratios (1:3, 1:1, and 3:1) on skin cell growth.

Taken together, the data showed that the ratio of the two acids alone was not the key factor in regulating skin cell growth; instead, a synergistic interaction was observed between oleic and linoleic acids, highlighting the importance of their co-existence in the vegetable oil or final dermal product. However, at higher concentrations (0.01 mg/100 µl) and after 72 hours, all three ratios tested significantly inhibited fibroblast growth while enhancing keratinocyte proliferation, highlighting the cell-type and dose-dependent specificity of the effect.

None of the vegetable oils tested showed a significant positive or negative effect on skin cell migration, and no significant changes in cell morphology were detected. In contrast, sterculic and oleic acids caused a significant decrease in skin cell migration. Linoleic acid also caused visible cell clustering and a local increase in density without slowing wound closure. This phenomenon, common to oleic acid and its mixtures, may indicate a change in cell organization during the healing process.

Notably, oleic and linoleic acids, either alone or in combination, induced the formation of cell clusters and an increase in cell density.

Significance of the study

The study results highlight the importance of plant oils and their components in enhancing skin regeneration and support their use in therapeutic and cosmetic skin care products.

According to the data obtained, the biological activity of these oils depends mainly on the fatty acid composition of the triglycerides. Complex interactions between these fatty acids determine the effect of plant oils on skin cell growth, which highlights the importance of knowing the exact chemical composition of plant oils. The study also revealed that unsaponifiable fractions of some oils, such as coconut and olive, can enhance fibroblast or keratinocyte growth at certain doses. In contrast, linden and calendula fractions inhibited fibroblast proliferation in some cases, highlighting the complex nature of these minor components.

Unsaponifiable compounds, although accounting for only about 1% of the oils, also showed a complex role: some (e.g. β-carotene and β-sitosterol) stimulated keratinocyte proliferation, while others (including ferulic acid and squalene) inhibited fibroblast growth, highlighting the need to consider their contribution along with fatty acids.

Limitations of the study

The study used skin cells grown in a laboratory setting for experimental purposes only. These cell culture models lack the complexity of the physiological skin environment, including the presence of immune cells, blood circulation, and barrier function. These factors highlight the need to validate the study results in animal models and human clinical trials, and to assess the safety and efficacy profile in real-world settings.

Additionally, the study used primary dermal fibroblasts from a single donor to ensure experimental consistency. Given this limitation, the researchers recommend that future studies include multiple donors to assess the reproducibility and generalizability of the results.