When the skin barrier is disrupted, moisturising the surface alone may not be enough. The skin barrier depends on an organised mixture of lipids in the stratum corneum, including ceramides, cholesterol and free fatty acids. Ceramides are particularly important because they contribute to the barrier and water-holding functions of the stratum corneum. Research has shown that differences in ceramide levels and ceramide species are associated with changes in skin barrier function and water retention. (Ishikawa et al., 2013).
This is why ingredients that can support the skin’s own ceramide production are scientifically interesting for dry and barrier-disrupted skin.
One such ingredient is Eucalyptus extract.
From Australia to Modern Skin Science
Eucalyptus is a large genus of plants belonging to the Myrtaceae family and is strongly associated with the Australian continent. Eucalyptus species have a long history of traditional use by Aboriginal communities. Scientific reviews have documented the use of eucalyptus leaves and preparations for various traditional applications, including wounds, cuts and other conditions where antiseptic and anti-inflammatory properties were considered useful. (Chandorkar et al., 2021).
The traditional use of eucalyptus is not, however, the reason we are particularly interested in it at smith-meyerlab. Modern research has provided a more specific explanation for its potential role in skin care: certain eucalyptus extracts can influence epidermal ceramide metabolism and skin barrier function.
Why Ceramides Matter
The stratum corneum forms the outermost functional barrier of the skin. Its barrier properties depend on the organisation of corneocytes surrounded by an extracellular lipid matrix containing ceramides, cholesterol and free fatty acids.
Research investigating ceramide profiles across different body sites and seasons found that ceramide composition is associated with transepidermal water loss and water-holding properties of the stratum corneum. This demonstrates that ceramides are not simply cosmetic moisturising ingredients; they are part of the biological structure responsible for maintaining skin barrier function. (Ishikawa et al., 2013).
When the barrier is compromised, maintaining an appropriate ceramide profile becomes particularly relevant because reduced or altered ceramide levels can be associated with dry, rough and poorly hydrated skin. In a study of winter dry skin, specific ceramide species were strongly associated with indicators of skin dryness and barrier function. (Ishikawa et al., 2013).
Eucalyptus Extract and Ceramide Production
The most important scientific evidence for eucalyptus and ceramides comes from a study by Ishikawa et al. (2012).
The researchers added eucalyptus extract to cultured human keratinocytes and observed a dose-dependent increase in ceramide levels. The extract also increased the biosynthesis of ceramide, glucosylceramide and sphingomyelin.
The researchers then investigated its effect on human skin with experimentally disrupted barrier function. Topical application of eucalyptus extract resulted in a significant increase in stratum corneum ceramide levels, together with improvements in water-holding and barrier functions. (Ishikawa et al., 2012).
This finding is important because it suggests that eucalyptus extract may support barrier recovery not merely by forming an occlusive layer over the skin, but by influencing the skin’s own lipid-production pathways.
How Does Eucalyptus Extract Promote Ceramide Synthesis?
Ceramide production in epidermal keratinocytes involves several enzymatic pathways.
In the study by Ishikawa et al. (2012), eucalyptus extract was associated with increased activity or expression of enzymes involved in ceramide metabolism, including serine palmitoyltransferase (SPT), acid sphingomyelinase, neutral sphingomyelinase, glucosylceramide synthase and glucocerebrosidase.
These enzymes participate in different pathways involved in the generation and processing of epidermal sphingolipids and ceramides. (Ishikawa et al., 2012).
The researchers also investigated individual constituents of the eucalyptus extract and identified macrocarpal A as an important candidate.
When macrocarpal A was added to cultured human keratinocytes, it increased ceramide levels and increased the expression of several enzymes associated with ceramide synthesis and metabolism. The authors therefore proposed that macrocarpal A may be a key component responsible for the ceramide-stimulating effect of the eucalyptus extract. (Ishikawa et al., 2012).
Macrocarpal A: The Interesting Chemical Constituent
Macrocarpal A belongs to a group of eucalyptus-derived acyl phloroglucinol compounds. It is a specialised phytochemical found in eucalyptus rather than one of the better-known volatile components associated with eucalyptus essential oil.
Chemical investigations of Eucalyptus globulus have identified macrocarpal A together with other constituents including macrocarpal B, betulinic acid, β-sitosterol, gallic acid and ellagic acid. (Yang & Guo, 2007).
Importantly, macrocarpal A has also been isolated from different eucalyptus species and belongs to a structurally related family of macrocarpal compounds. (Alliot et al., 2013).
For skin-barrier science, macrocarpal A is particularly interesting because the ceramide study demonstrated a direct biological effect of the compound on cultured human keratinocytes. It increased ceramide levels and influenced the expression of enzymes involved in ceramide metabolism. (Ishikawa et al., 2012).
An important distinction
Eucalyptus contains many different chemical constituents, and the composition varies according to the species and extraction method.
The volatile essential oil fraction commonly contains compounds such as 1,8-cineole (eucalyptol), α-pinene and limonene, among others. However, the published research specifically linking eucalyptus to increased ceramide synthesis identified macrocarpal A, rather than 1,8-cineole, as a key candidate responsible for this activity. (Ishikawa et al., 2012).
Therefore, it would be scientifically inaccurate to simply state that “eucalyptus oil increases ceramide” or that “1,8-cineole stimulates ceramide synthesis.” The evidence is more specifically associated with eucalyptus extract and its non-volatile constituents, particularly macrocarpal A.
Evidence in Dry and Barrier-Disrupted Skin
The biological effect of eucalyptus extract has also been investigated beyond cell culture.
Ishikawa et al. (2013) studied people with winter dry skin and found that specific ceramide species were associated with the severity of dryness, roughness, scaling and water-holding function. After 28 days of treatment with a moisturiser containing eucalyptus extract, one specific ceramide species, CER[NP], increased. The treatment was also associated with improvements in skin conductance and transepidermal water loss during the follow-up period. (Ishikawa et al., 2013).
These findings support the concept that the quality and composition of ceramides matter, not simply the total amount of ceramide present in the skin.
This is particularly relevant when developing products for dry or compromised skin because barrier recovery is a biological process rather than simply a matter of adding surface moisture.
Why This Matters for Cheilitis
Cheilitis and chronically chapped lips can involve disruption of the lip barrier, resulting in dryness, scaling, discomfort and increased susceptibility to environmental stress.
The lips also have anatomical and physiological characteristics that distinguish them from typical skin. Research examining ceramide profiles across different body regions has shown that the ceramide profile can vary according to anatomical location, including the lips. (Ishikawa et al., 2013).
For a barrier-compromised lip, therefore, a daily product should do more than simply provide a temporary sensation of softness.
A useful approach is to provide surface protection and emolliency while supporting the biological processes involved in barrier maintenance.
This is where the concept of ceramide-supporting ingredients becomes relevant.
Why It Matters to smith-meyerlab
At smith-meyerlab, we look at ingredients from a formulation and skin-function perspective rather than simply asking whether an ingredient is trendy.
This is exactly why eucalyptus extract has a place in our CERA-K Recovery Lip Balm.
The lips are particularly vulnerable to barrier disruption. Unlike much of the skin on the body, the lip vermilion has a thinner and more vulnerable barrier and is exposed continuously to environmental stress, saliva, licking, friction and dryness.
For people experiencing cheilitis or chronically chapped, dry and compromised lips, recovery is not simply about making the lips feel greasy or temporarily soft.
The objective is to support the recovery and maintenance of the compromised barrier.
CERA-K Recovery Lip Balm therefore combines a lipid-rich ointment-based format for daily protective care with selected barrier-supporting ingredients, including eucalyptus extract, to support the skin’s natural recovery process.
The scientific interest in eucalyptus extract is particularly relevant because it provides a different approach to barrier support, not only supplying lipids from the outside, but potentially encouraging the skin to produce more of its own ceramides.
This fits the philosophy behind CERA-K: recovery is not just about covering the problem. It is about supporting the biology of the barrier.
References:
- Alliot, J., Gravel, E., Larquetoux, L., Nicolas, M., & Doris, E. (2013). Semisynthesis of macrocarpal C and analogues by selective dehydration of macrocarpal A or B. Journal of Natural Products, 76(12), 2346–2349.
- Ishikawa, J., Shimotoyodome, Y., Chen, S., Ohkubo, K., Takagi, Y., Fujimura, T., Kitahara, T., & Takema, Y. (2012). Eucalyptus increases ceramide levels in keratinocytes and improves stratum corneum function. International Journal of Cosmetic Science, 34(1), 17–22.
- Ishikawa, J., Yoshida, H., Ito, S., Naoe, A., Fujimura, T., Kitahara, T., Takema, Y., Zerweck, C., & Grove, G. L. (2013). Dry skin in the winter is related to the ceramide profile in the stratum corneum and can be improved by treatment with a Eucalyptus extract. Journal of Cosmetic Dermatology, 12(1), 3–11.
- Ishikawa, J., Shimotoyodome, Y., Ito, S., Miyauchi, Y., Fujimura, T., Kitahara, T., & Hase, T. (2013). Variations in the ceramide profile in different seasons and regions of the body contribute to stratum corneum functions. Archives of Dermatological Research, 305(2), 151–162.
- Yang, X.-W., & Guo, Q.-M. (2007). Studies on chemical constituents in fruits of Eucalyptus globulus. Zhongguo Zhong Yao Za Zhi, 32(6), 496–500.
- Chandorkar, N., Tambe, S., Amin, P., & Madankar, C. (2021). A systematic review on the medicinal properties of Eucalyptus species. PhytomedPlus, 1(4)
