The evidence is strongest for injectable hyaluronic acid treatments, followed by topical applications. Oral hyaluronic acid shows positive signals for hydration and elasticity in small trials, but the evidence base is still limited and it adds nothing demonstrable on top of collagen. Multiple studies have been funded by manufacturers, which may cast their outcomes in a favourable light.
Topically applied hyaluronic acid, such as in creams and serums, shows positive effects on skin hydration and the visible reduction of wrinkles in multiple clinical studies. A literature review concludes that it is well tolerated and effective as a support for skin rejuvenation1,2. An important caveat: one of the authors of that review is employed by L'Oréal, the manufacturer of the product studied. This represents a serious conflict of interest and calls for caution when interpreting those specific conclusions. The remaining clinical studies do support the effect on hydration, but the exact magnitude varies.
Injected hyaluronic acid, both as a classic dermal filler and as a micro-filler treatment, has the strongest evidence base. In a randomised controlled trial with 146 participants, superficial wrinkles on the face, neck and décolleté decreased significantly after a series of micro-filler injections, visible at day 75 and day 120 compared with cream alone3. Skin hydration improved measurably, but that effect was particularly short-lived following the injection. Side effects were mild and resolved within 48 hours. This study was funded by the manufacturer of the product (FILLMED). The classic hyaluronic acid filler is the most widely used dermal filler worldwide: it improves wrinkles and volume loss, attracts water and is in principle reversible with an enzyme injection (hyaluronidase), which makes it relatively safe4. In a smaller split-face study (27 participants), non-crosslinked hyaluronic acid improved hydration and elasticity around the eye, but the effect diminished over time, and for skin roughness a polynucleotide filler performed better5.
For oral hyaluronic acid as a supplement, the picture is more nuanced. A meta-analysis of seven randomised controlled trials shows statistically significant improvements in skin hydration, elasticity and wrinkle depth6. At the same time, effects on skin firmness, wrinkle volume and transepidermal water loss were not significant. The researchers themselves caution that participant numbers are small and that the studies vary considerably from one another; they call for larger trials. Oral hyaluronic acid therefore appears to have some effect, but the evidence is preliminary.
A notable finding concerns the added value of oral hyaluronic acid combined with collagen and vitamin C. In a rigorous double-blind, placebo-controlled RCT with 87 women over 16 weeks, the combination of collagen with vitamin C improved the skin noticeably, but adding oral hyaluronic acid to that supplement provided no measurable additional benefit for hydration, elasticity or any of the other measured parameters7. Those who already take a collagen supplement therefore appear to have little to gain by also adding oral hyaluronic acid.
Finally, a review article on so-called 'skin boosters' containing hyaluronic acid has been retracted by the publisher and therefore does not count as a reliable source8. This is worth mentioning because articles of this kind sometimes appear in promotional materials.
Based on one meta-analysis (oral HA, 7 RCTs), three clinical RCTs or controlled studies (injectable/topical), one literature review with possible commercial bias (L'Oréal author), one small split-face study (n=27) and one retracted review (excluded). One study funded by the manufacturer (FILLMED). Total participant numbers estimated on the basis of available data.