When applied topically, hyaluronic acid is an active ingredient known for its excellent tolerability.
It is suitable for all skin types, including sensitive, atopic, or redness-prone skin. Moreover, this active ingredient is neither irritating, nor allergenic, nor photosensitizing, making it a safe option in any season, even before sun. Furthermore, European cosmetic regulations do not impose a maximum concentration for this ingredient. In practice, formulations typically use the hyaluronic acid at concentrations ranging from 0.1% to 3%, depending on the desired effect. Whether incorporated into a serum, cream, or mask, it can be used daily with confidence.
Side effects associated with hyaluronic acid are very rare and limited to mild redness that may correspond to an allergic reaction. A study conducted by TORT and KARAKUCUK assessed the tolerability of various serums containing 0.5%, 1%, or 2% of hyaluronic acid of low molecular weight (400 kDa). These serums were applied under occlusion to the forearms of 15 volunteers for durations of 30 minutes, 72 hours, 96 hours, and 7 days. No signs of irritation were observed in any participants, even with the higher concentration formulations or after a week of occlusion. Although the small sample size limits the scope of the conclusions, this study is reassuring regarding the good tolerability of hyaluronic acid.
Hyaluronic acid present in topical skincare products is also considered safe for pregnant or breastfeeding women. A review by the Scientific Committee for Consumer Safety (CSSC), an independent scientific committee managed by the European Commission, compiled data from about ten studies on the safety of using hyaluronic acid during pregnancy. These studies were conducted on rats or rabbits and, in the vast majority of cases, no side effects or fetal abnormalities were observed. However, in one trial where rats received up to 60 mg/kg body weight of a 1 % hyaluronic acid solution by subcutaneous injection, nodular hyperplasia of the reticular zone cells was present in the adrenal glands of the treated mothers.
It is important to put this result into context: this finding comes from a single animal study in which the product was administered by injection rather than topically. To date, hyaluronic acid has been used for several decades in cosmetic products, with no reported adverse effects in pregnant or nursing women, nor in their children. Although no clinical trials have been conducted in pregnant women for obvious ethical reasons, the available data and its long-standing use support its good tolerability. As always, however, it remains advisable to consult a healthcare professional before any application, especially on damaged skin or simply when in doubt.