Hyaluronic acid, a popular skincare ingredient, doesn’t hold 1000 times its weight in water, despite frequent marketing claims.

The ingredient is a humectant, a substance that attracts moisture. Applied topically, it can improve skin hydration, enhance elasticity and reduce wrinkle depth.

But chemists have long suspected that the idea it can hold 1000 times its weight in water is too much of a stretch. The claim has been cited for decades,…