According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized, double-blind, placebo-controlled trial
In Japanese adults with clinically diagnosed dry skin, participants receive either 120–240 mg/day of oral hyaluronan or a matching placebo for 4–6 weeks, with skin moisture measured by Corneometer® at baseline, week 2, week 4, and week 6 in both facial and arm regions. Systematic review with meta-analysis of RCTs
A systematic review identifying all published randomized, double-blind, placebo-controlled trials in Japanese adults with dry skin that tested oral hyaluronan (120–240 mg/day) for 4–6 weeks and reported Corneometer® skin moisture outcomes in facial and arm regions, with pooled effect size analysis. Parallel-group RCT with extended follow-up
A parallel-group RCT in Japanese adults with dry skin comparing 120 mg/day vs. 240 mg/day hyaluronan vs. placebo over 6 weeks, measuring Corneometer® skin moisture at baseline and weekly, with follow-up at 2 weeks post-intervention to assess persistence of effect. Single-center RCT with standardized protocol
A single-center RCT in Japan using standardized diagnostic criteria for dry skin, standardized Corneometer® measurement protocols on facial and arm sites, and consistent hyaluronan formulation (120–240 mg/day) over 4–6 weeks, with blinding confirmed and adherence monitored. Observational cohort study with matched controls
An observational cohort study in Japanese adults with dry skin comparing those who self-reported daily hyaluronan intake (120–240 mg/day) for 4–6 weeks with matched controls, measuring Corneometer® skin moisture at baseline and endpoint, adjusting for confounders like humidity, skincare routines, and age.