Hyaluronic acid is one of the most popular ingredients in cosmetics. It appears in serums, creams, masks, and patches, and also—increasingly—in oral supplements. But not all hyaluronic acid works in the same way, and the distinction between topical and oral is not just a matter of format: it's a difference in mechanism and where it acts on the skin.
What is hyaluronic acid and what does it do for the skin?
Hyaluronic acid (HA) is a glycosaminoglycan—a polysaccharide—naturally present in the body, with a particular concentration in the skin, joints, and the vitreous humor of the eye. In the skin, HA is distributed in the dermis and epidermis, where it acts as a water reservoir: a single HA molecule can retain up to 1,000 times its weight in water, making it the main regulator of dermal hydration.
With age—and especially from perimenopause onwards—HA synthesis progressively decreases. The activity of hyaluronidase (the enzyme that degrades it) increases. The result is skin that loses its ability to retain water in the dermal layers, even if it is well hydrated on the surface.
Is oral hyaluronic acid absorbed? What studies say
For years, there was debate about whether oral HA could be usefully absorbed, given that it is a large molecule. More recent studies have partly resolved this question: low molecular weight HA (<10 kDa) is absorbed in the small intestine and can be detected in the blood and peripheral tissues, including the skin, within hours of ingestion. High molecular weight HA is partially hydrolyzed in the intestine before absorption.
The study by Michelotti et al. (2021) showed significant improvements in skin hydration, wrinkle reduction, and skin radiance in women who took oral HA for 12 weeks, compared to placebo. Kawada et al. (2015) observed improvements in stratum corneum hydration and reduction in skin dryness with 120 mg/day of HA in a double-blind trial. LEVIAL includes 45 mg of sodium hyaluronate per vial.
Differences in molecular weight and their effect on efficacy
The molecular weight of HA determines both its oral absorption pathway and its topical mechanism of action. High molecular weight HA (>1,000 kDa) creates a hydrating film on the skin's surface but does not penetrate the epidermis; it has an immediate and visible but superficial hydrating effect. Low molecular weight HA (<100 kDa) penetrates the epidermis better and reaches deeper layers; its hydrating effect is less immediate but longer-lasting.
Orally, low molecular weight HA has better bioavailability and a greater ability to reach the dermis via systemic circulation. This distinction is relevant for interpreting supplement labels: it's not enough for them to contain HA; the molecular weight determines its action profile.
Oral vs. topical: distinct but not contradictory routes of action
Topical HA acts on the surface and in the most superficial layers of the epidermis, providing immediate hydration and improving texture. Oral HA reaches the dermis through the bloodstream, where it can contribute to supporting structural dermal hydration and stimulating endogenous HA synthesis by fibroblasts. These are two complementary mechanisms that act on different layers.
The most coherent logic is not to choose between one and the other, but to combine them: a good topical HA serum for superficial hydration and an oral HA supplement for deep dermal support. This is exactly the same inside-out logic that articulates the LEVIAL approach.
In what contexts does oral supplementation make the most sense?
Oral HA supplementation makes particular sense for skin with persistent structural dryness that does not respond well to topical hydration; during periods of increased demand (menopause, mature skin from age 40 onwards); and when a sustained effect on deep dermal density and hydration is sought, not just on the surface. In these contexts, internal support adds what cosmetics alone cannot provide.
