Researchers at the University of Phayao, the College of Herbal Pharmacy of Thailand, and Mae Fah Luang University examined the stability, bioactivity, and dermal safety of Prunus leaf extracts when formulated into a cream.
The work compared ethanolic extracts from the leaves of three plum species — Prunus domestica (European plum, EL), Prunus salicina (Japanese plum, JL), and Prunus cerasifera (cherry plum, CL) — to identify the most promising extract for cosmetic use.
The team then developed a topical cream containing the selected extract and evaluated its antioxidant retention, skin penetration, and safety in a human clinical study.
Plum species are widely cultivated across Europe, Asia, and the Americas for their fruit, but the leaves are typically discarded after harvest. These leaves are rich in compounds such as phenolics, flavonoids and condensed tannins, which are linked to antioxidant, anti-inflammatory, and photoprotective effects.
Among these, the flavonoid rutin is particularly valued for its ability to neutralise free radicals, protect against UV-induced damage, reduce redness and irritation, and even support skin-brightening formulations.
Bioactivity differences among Prunus species
The study showed clear differences between the three Prunus species. While JL extract contained the highest total phenolic content, CL extract had the highest level of condensed tannins, a class of polyphenols with strong antioxidant and anti-inflammatory effects.
In antioxidant testing, CL extract delivered the strongest results. This suggested that tannins, more than total phenolics alone, played a central role in driving antioxidant bioactivity.
Previous research has identified rutin as a key flavonoid in Prunus leaves, with broad cosmetic potential due to its ability to combat oxidative stress, inhibit tyrosinase, and modulate inflammation.
However, this study underlined that condensed tannins contributed significantly to antioxidant effects as well. The researchers noted that CL’s higher tannin content likely explained its superior lipid protection, despite having lower phenolic levels than JL.
Stability under storage conditions
The extracts were subjected to different storage conditions — refrigerated (4°C), ambient (25°C), and accelerated heat stress (45°C) — over a 60-day period.
All extracts experienced losses in total phenolics, tannins, and antioxidant activity under heat stress, with degradation beginning as early as the seventh day at 45°C.
Refrigeration best preserved the extracts, retaining 70% to 80% of their phenolic content after two months.
Among the species, CL extract was more prone to degradation at higher temperatures, which the researchers attributed to its higher levels of reactive compounds such as tannins and rutin.
Despite this sensitivity, CL consistently maintained stronger antioxidant activity than the other extracts across all conditions. Based on this profile, it was chosen for incorporation into a topical cream.
Formulation performance
The team developed a cream formulation containing 0.3% w/w CL extract (referred to as CCL) and evaluated its physical and chemical stability. The cream remained stable for 60 days at room temperature, showing no phase separation, colour change, or significant pH drift.
Under thermal cycling conditions (alternating between 45°C and 4°C) the formulation still retained over 74% of its antioxidant activity after 24 days. At room temperature, antioxidant retention was above 80% after two months.
These findings indicated that while heat accelerated degradation, the formulation offered acceptable stability for commercial use under standard storage conditions.
The researchers suggested that advanced stabilisation techniques, such as encapsulation, could be explored to further improve long-term antioxidant retention in hot climates or during transport.
Skin penetration and retention
To test delivery, the cream was applied to a synthetic Strat-M membrane in Franz diffusion cells. The results showed that rutin from the CCL cream was retained in the membrane at levels 5.7 times higher than those from an aqueous extract control.
However, no rutin was detected in the receptor chamber, indicating that the compound did not permeate through the membrane into deeper layers.
This limited penetration aligned with the known properties of rutin, which has a relatively high molecular weight and low lipid solubility, restricting its ability to pass through the stratum corneum.
Instead, rutin tends to localise at the skin surface, where it can still deliver antioxidant and protective effects.
The use of formulation excipients, such as silicones and propylene glycol, may have contributed to the enhanced cutaneous retention observed with CCL, supporting its potential as a topical antioxidant active.
Clinical safety evaluation
The dermal safety of the cream was tested in a double-blind, semi-open patch test involving 26 healthy volunteers aged 30 to 50 years.
Participants received applications of the CCL cream, the extract alone, the cream base, deionized water (negative control), and sodium lauryl sulfate (positive control).
The patches were applied for 48 hours, and a dermatologist used a standard scoring criteria to assess skin responses for redness and swelling.
The results showed no irritation or adverse reactions for the extract, cream base, or CCL cream. The Primary Dermal Irritation Index (PDII) for all three was below 0.5, classifying them as non-irritating.
In contrast, sodium lauryl sulfate produced a PDII of 1.83, confirming its expected irritant effect. Measurements of erythema using a skin probe further supported these findings, with any mild redness returning to baseline within 48 hours for the test formulations.
Conclusion
This research presents a compelling case for the inclusion of Prunus cerasifera leaf extract in cosmetic formulations.
Among the three species studied, CL extract delivered the best balance of tannin content, antioxidant activity and bioactive retention, despite being more temperature-sensitive than other species.
When incorporated into a cream, the extract proved physically and chemically stable, showed enhanced cutaneous retention, and was confirmed safe for human use with no signs of irritation.
For the cosmetics and personal care industry, the study demonstrated the dual benefits of efficacy and sustainability.
Source: Cosmetics
“Stability, Bioactivity, and Skin Penetration of Prunus Leaf Extracts in Cream Formulations: A Clinical Study on Skin Irritation”
https://doi.org/10.3390/cosmetics12040146
Authors: Lapatrada Mungmai, et al.
