Which other active ingredients can polyglutamic acid be combined with?

The polyglutamic acid is often compared to hyaluronic acid. These two active ingredients differ in their molecular weight, chemical structure, and origin: hyaluronic acid is naturally produced by the body, particularly by the skin's fibroblasts, while polyglutamic acid is obtained following the fermentation of certain bacteria, such as the Gram-positive bacterium Bacillus subtilis.

The polyglutamic acid and the hyaluronic acid have complementary hydrating effects.

Combining these two active ingredients is particularly beneficial for providing comprehensive hydration to the skin and reducing dehydration fine lines. Polyglutamic acid has a strong humectant power and can retain up to 5,000 times its weight in water. However, its significant molecular weight prevents it from penetrating deeply into the epidermis. It therefore acts more on the surface and forms a continuous film that traps moisture. Hyaluronic acid, on the other hand, is capable of binding up to 1,000 times its weight in water. Moreover, depending on its molecular weight, it can penetrate more or less deeply into the epidermis and support the production of hyaluronic acid by fibroblasts. This synergy between polyglutamic acid and hyaluronic acid provides the skin with a multilayer hydration, with action both on the surface and deeper down, particularly sought after by dehydrated skin prone to tightness.

Pairing polyglutamic acid with retinol, one of the most studied cosmetic actives, offers dual benefits: achieving better results and minimising side effects. Indeed, retinol, a derivative of vitamin A, is known for stimulating cell renewal, promoting collagen synthesis, and improving skin texture. However, its effectiveness is often accompanied by a transient irritation phase, particularly in sensitive skin. Redness, burning sensations, and excessive peeling are common skin manifestations observed when starting to use retinol.

In this context, due to its strong hygroscopic power and its ability to form a protective but non-occlusive film on the skin's surface, polyglutamic acid emerges as an ally. By enhancing skin hydration and its barrier function, it helps to reduce skin reactivity caused by retinol and improves the tolerance of this active ingredient. Furthermore, its hydrating properties enable it to assist in smoothing out dehydration fine lines, complementing the deeper action of retinol on skin ageing.

The combination of polyglutamic acid and collagen presents another interesting synergy for improving skin hydration and structure. While polyglutamic acid primarily works on the surface to limit water loss, the collagen operates at multiple levels, provided it is used in a low molecular weight form, that is, hydrolysed, in order to cross the skin barrier. Studies have indeed shown that this collagen can stimulate the proliferation and activity of dermal fibroblasts, thus promoting the natural production of collagen, elastin and hyaluronic acid. Collagen also promotes better cell-to-cell adhesion, thereby strengthening the integrity of the epidermal barrier. These actions are effectively complemented by those of polyglutamic acid, which retains water on the surface and limits its evaporation. Together, they form a true hydration shield.

Important : To achieve the effects outlined above, it is necessary for the collagen used in skincare treatments to be hydrolysed in order to reach a peptide size less than 6 kDa. Beyond this, it fails to penetrate the skin barrier and remains on the skin's surface.

It is also possible to combine polyglutamic acid with niacinamide, an active and stable form of vitamin B3. While polyglutamic acid has a very good ability to retain water on the surface of the epidermis, niacinamide works more deeply to rehydrate the skin. Several studies have shown that this molecule can increase the rate of biosynthesis of ceramides, cholesterol, free fatty acids, as well as other fractions of epidermal sphingolipids in the horny layer, lipid compounds playing a central role in the structural and functional integrity of the skin barrier function. Niacinamide and polyglutamic acid thus have a complementary hydrating role.

Niacinamide is also recognised for its anti-inflammatory, antioxidant, and depigmenting properties. It modulates the release of pro-inflammatory interleukins, limits cellular oxidation, and inhibits the transfer of melanosomes to keratinocytes, making it an ideal active ingredient for skin prone to redness or hyperpigmentation. By maintaining optimal hydration, polyglutamic acid supports the action of the niacinamide and reduces the irritations sometimes observed at high concentrations.

Combining polyglutamic acid with vitamin C or its derivatives can also be beneficial, offering both hydration and protection against oxidative stress. Indeed, vitamin C is one of the most well-documented antioxidant agents and is not only capable of neutralising free radicals, but also inhibiting tyrosinase, a key enzyme in melanogenesis, and stimulating collagen synthesis, making it an ideal ingredient for correcting uneven skin tone and preventing photoaging. However, its high reactivity and acidic pH, particularly when it comes to pure vitamin C, can make it irritating for sensitive skin.

To mitigate the side effects associated with vitamin C, it may be beneficial to combine it with polyglutamic acid. As a high molecular weight humectant, it forms a protective film on the skin's surface, reducing water evaporation and lessening the tightness that vitamin C formulas can induce. Furthermore, this hydrating film helps to strengthen the integrity of the skin barrier, which enhances the overall tolerance of the treatment.

Polyglutamic acid and red algae extract form another beneficial combination to enhance skin hydration. Indeed, carrageenan extracted from red algae is capable of stimulating the synthesis of hyaluronic acid, thus enhancing natural skin hydration. Moreover, studies have shown that this botanical ingredient can stimulate the synthesis of ceramides, which strengthen the skin's barrier and limit insensible water loss. As a reminder, ceramides are lipids organised into dense and structured lamellae that form the intercellular cement. The surface hydrating effects of polyglutamic acid complement the properties of red algae extract to improve skin hydration and barrier function.

Finally, the combination of polyglutamic acid and duckweed represents a promising new partnership to address the needs of dehydrated and/or sensitive skin. Also known as water lentil, or Spirodela polyrhiza, the duckweed is an aquatic plant known for its richness in polysaccharides, particularly apiogalacturonans, pectins with a strong hygroscopic power. These molecules are primarily released during the controlled hydrolysis of the plant, a process in which its cell walls are fragmented to recover the most active soluble fraction. When combined with polyglutamic acid, the duckweed could see its moisturising potential enhanced.

Furthermore, the duckweed has an interesting anti-inflammatory activity. It is notably capable of reducing the levels of certain cytokines, such as TNF-α and IL-6, but also of inhibiting the infiltration and degranulation of mast cells, thus reducing the skin's allergic and inflammatory responses. The duo of polyglutamic acid and duckweed could therefore target both dehydration and skin irritations.

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