What are the skin benefits of Spirodela polyrhiza?

All skin types require hydration, including oily skin, contrary to some misconceptions. The Spirodela polyrhiza can help maintain skin hydration by increasing the water reserves of the stratum corneum. Indeed, the spirodela is a highly hygroscopic active ingredient, a property derived from its high concentration of apiogalacturonans, compounds belonging to the pectin family. These molecules have a strong ability to attract and retain water. An in vitro study has shown that on average, each apiogalacturonan can bind to 23 water molecules. Spirodela can also enhance the activity of aquaporin-3, protein channels that conduct water through skin cells.

Similar to aloe vera gel, hyaluronic acid, or polyglutamic acid, the Spirodela polyrhiza appears to be a promising hydrating agent for dehydrated skin.

A non-independent study recently highlighted the strong hydrating capacity of the spirodela. For this, 16 volunteers were recruited. The water content of the stratum corneum and the upper dermis was measured before and after the application of a 3% spirodela emulsion. The results after three and six hours are reported in the table below. The long-term effects of spirodela on skin hydration were also tested with 31 volunteers. After 42 days of daily use of the treatment, a 10% increase in skin hydration was measured.

Redness, itching, minor skin irritations... The signs of skin inflammation are numerous. There are reasons to believe that duckweed could alleviate them. Several studies have shown that this active ingredient is capable oflowering the levels of inflammatory cytokines, such as tumour necrosis factor alpha, interleukin-6 and interferon-γ. The Spirodela polyrhiza also inhibits the infiltration and degranulation of mast cells, thus reducing the skin's allergic and inflammatory responses. Finally, this extract from the water lentil helps to restore certain skin barrier proteins, like filaggrin, sirtuin-1 and claudin-1, which are essential for maintaining healthy and resilient skin.

There are a few studies that have shown that duckweed can reduce the symptoms of atopic dermatitis, an inflammatory skin condition characterised by redness, skin dryness and varying degrees of itching. Although these studies were conducted on mice and not humans, which limits their transferability, they provide an interesting initial insight. One such study can be cited, conducted with 100 mice in which eczema was induced using 2,4-dinitrochlorobenzene (DNCB). The application of solutions with varying concentrations of Spirodela polyrhiza (1 to 100 mg/mL) allowed for a dose-dependent decrease in serum levels of immunoglobulin E, antibodies associated with eczema. A decrease in mast cell infiltration, as well as the expression of pro-inflammatory cytokines (IL-4, IL-6, TNF-α), was also recorded.

By modulating the release of pro-inflammatory mediators, the Spirodela polyrhiza can help to alleviate skin irritations.

Spirodela appears to be a relevant active ingredient for protecting the skin against free radicals. As a reminder, these are unstable compounds naturally generated during metabolism but also following exposure to UV rays or pollution. Their number is normally regulated through antioxidant enzymes present in the skin, but sometimes these can be overwhelmed. Free radicals then have free rein to oxidise lipids, proteins and DNA in cells, thus promoting the occurrence of certain chronic diseases, as well as premature skin ageing.

Studies highlighting the antioxidant properties of Spirodela polyrhiza are still scarce. However, we can mention the work carried out by JANG and his team in 2009 on human HaCaT keratinocytes. The addition of a methanol extract of Spirodela polyrhiza at 50 and 400 µg/mL to the culture medium showed a significant protective effect against 500 µM of hydrogen peroxide (H2O2). The spirodela not only allowed the cells to survive but also significantly inhibited the release of the enzyme lactate dehydrogenase and DNA fragmentation by H2O2. It also demonstrated free radical scavenging activities, notably of DPPH and superoxide radicals. It would be interesting for more work to be carried out to better understand the antioxidant effects of spirodela, but this study is encouraging.

It is known that sun exposure can be harmful to the skin, ranging from simple redness to melanomas and carcinomas, including varying degrees of sunburn. However, the sun's impact on the skin does not stop there and can also result in premature skin sagging accompanied by brown spots. This is referred to as photoaging. There are reasons to believe that duckweed could help prevent this phenomenon. Indeed, in addition to its antioxidant effects, which are already useful for delaying the appearance of wrinkles, this active ingredient would have tightening and depigmenting effects.

Researchers aimed to evaluate in vitro several biological parameters related to skin sagging and hyperpigmentation. They measured the ability of the spirodela to stimulate pro-collagen synthesis, inhibit the activity of the proteolytic enzyme MMP-1, involved in the degradation of dermal collagen, reduce melanin synthesis, and lower the activity of tyrosinase, a key enzyme in melanogenesis. The scientists focused on two 25 µg/mL solutions of spirodela, called SE and SEE. SE is an extract obtained with a hydroalcoholic solution (70% ethanol). It contains compounds soluble in water and alcohol. SEE corresponds to a fraction of SE, specifically extracted using ethyl acetate, an organic solvent. This fractionation step allows only semi-polar compounds, often more biologically active, to be isolated. The results obtained by the researchers are presented in the table below and show interesting tightening and depigmenting effects of the Spirodela polyrhiza.

Finally, the aforementioned non-independent study did not solely focus on the hydrating effects of the Spirodela polyrhiza but also its ability to reduce wrinkles. For this, 31 volunteers with an average age of 51 applied a daily emulsion containing 3% spirodela. After 42 days, a significant reduction of 7.4% in crow's feet wrinkles was measured.

Even though more studies still need to be conducted, duckweed appears to be a relevant active ingredient in combating photoaging.

• JANG S. & al. Antioxidative and Acute Anti-inflammatory Effects of Spirodela polyrhiza Extract in Human HaCaT Keratinocytes and NC/Nga Mice (2009).

• YANG W. M. & al. Improvement of atopic dermatitis with topical application of Spirodela polyrhiza. Journal of Ethnopharmacology (2016).

• KIM S. G. & al. Whitening and anti-wrinkle effect of Spirodela polyrhiza extracts. Journal of Applied Biological Chemistry (2019).

• KIM S. H. & al. A combination of Olea europaea leaf extract and Spirodela polyrhiza extract alleviates atopic dermatitis by modulating immune balance and skin barrier function in a 1-chloro-2,4-dinitrobenzene-induced murine model. Phytomedicine (2021).

• CLOSS B. & al. Highlighting the hygroscopic capacities of apiogalacturonans. Journal of Molecular Graphics and Modelling (2023).

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