What are the benefits of collagen for the skin?

Collagen is the most abundant protein in the human body, comprising nearly a quarter of the total protein content.

Synthesised by fibroblasts, it constitutes the framework of connective tissues, including the skin, bones, tendons and ligaments, and endows them with mechanical strength and flexibility. Of the 28 identified collagen types, type I is the most abundant in the dermis, where it accounts for around 80 to 90% of total collagen. Its triple-helical structure, rich in glycine, proline and hydroxyproline, allows it to assemble into robust fibres, a property essential to skin cohesion.

With age, the production of collagen decreases progressively and the fibres become stiffer and more fragmented. Thus, from the age of 25, a loss of around 1% per year is observed. This decline, exacerbated by exposure to UV rays, tobacco, pollution and by glycation, a process corresponding to the stiffening of fibres due to glucose, is partly responsible for the appearance of wrinkles on the skin, as well as the loss of its firmness.

The collagen has become an extremely popular active ingredient in cosmetics, especially in treatments designed to slow skin ageing. This popularity is explained by a clear objective: to offset the gradual decline in skin collagen with age, a phenomenon that contributes to loss of firmness, elasticity and the appearance of wrinkles. Incorporated into numerous serums, creams and masks, the topical collagen is presented as an ally to reinforce the skin’s structure and improve hydration.

• Collagen exhibits antioxidant properties.

  Topical collagen initially has an interesting antioxidant activity to limit certain mechanisms involved in cutaneous ageing. By neutralising part of the free radicals generated by UV exposure, pollution or certain endogenous metabolic reactions, it helps reduce the cellular damage responsible for the alteration of dermal fibres and the loss of skin firmness.

  Several studies in vitro have shown that peptides derived from collagen can act as free radical scavengers. A study on hydrolysed collagen from sheep skin demonstrated that the more extensively the collagen was hydrolysed, the greater its antioxidant activity. The ABTS and DPPH assays — two standard methods for assessing a compound’s ability to stabilise free radicals — showed maximum activity after 4 hours of hydrolysis, reaching 67.6% neutralisation for ABTS and 52.75% for DPPH.

The study also highlights that reducing the molecular weight of peptides plays a decisive role: the shorter the collagen fragments, the higher their antioxidant capacity. When used daily, this form of collagen thus represents a valuable aid in preventing skin ageing.

• Collagen has hydrating properties.

  The moisturising properties of collagen applied to the skin are due to several complementary mechanisms. Firstly, this active ingredient forms a thin film on the surface of the epidermis that limits transepidermal water loss and protects the skin from external aggressors. Furthermore, thanks to its structure rich in hydrophilic amino acids, it attracts and retains water molecules in the superficial layers, thereby helping to maintain adequate hydration in the stratum corneum. Finally, collagen helps improve adhesion between epidermal cells, a process essential to the integrity of the skin barrier : the more cohesive the cell-cell junctions, the more effectively the skin retains water.

  The interest in the topical application of collagen and its effect on hydration have been assessed in various studies, including one conducted with individuals with sensitive and atopic skin. In this double-blind, placebo-controlled, randomised trial, 40 women with this skin type applied for four weeks a skincare product containing a gluco-oligosaccharide and a collagen tripeptide or the same cream without these actives. Several skin parameters were measured before and after use, including hydration level and insensible water loss. The results showed significantly greater improvements in the group that received the active-ingredient cream compared with the placebo.

• Collagen is believed to have restructuring effects.

  Topical collagen is often presented as a restructuring active ingredient, that is, capable of supporting the skin’s extracellular matrix. This matrix, composed primarily of collagen, elastin and glycoproteins such as versican, provides mechanical strength, cohesion and elasticity to tissues. As noted previously, with age and repeated environmental assaults, fibroblast activity decreases and the protein fibres underpinning the extracellular matrix become more rigid, fragment and become disorganised. However, collagen peptides are thought to have the capacity to stimulate these dermal cells, thus promoting skin regeneration and maintaining tissue structure.

  To better understand this restructuring potential, a study in vitro assessed the effect of collagen peptides on human dermal fibroblasts. In this study, the fibroblasts were exposed to 0.01% collagen peptides for 24 hours, then the researchers measured the expression of three extracellular matrix genes: COL1A1, encoding type I collagen, ELN, encoding elastin, and VCAN, encoding versican. The results demonstrate a clear stimulation of fibroblast activity.

However, it is important to note that native collagen is a fibrous protein whose high molecular weight (300 kDa) prevents its passage through the epidermal barrier. Thus, to be properly absorbed, it must be hydrolysed into collagen peptides with a molecular weight between 2,000 and 6,000 Da.

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