β-Glucan / Carboxymethyl Glucan
A polysaccharide — a chain of glucose units — drawn from oats, barley, yeast, mushrooms or algae. It's a heavyweight humectant, with some studies putting its water-binding above hyaluronic acid at matched concentrations, that also lays down a soothing surface film, reinforces the barrier, and brings antioxidant and anti-inflammatory activity that calms redness and reactive skin. Larger forms can engage the skin's immune cells to support repair, and there's early evidence for softening wrinkle depth.
Most formulas use it at or below 1% — and that's plenty. Below the 1% line isn't fairy-dusting for a humectant polysaccharide that genuinely works at low doses. Look for it high on the ingredient list (or named as sodium carboxymethyl beta-glucan) rather than chasing a big number.
Apply a serum or essence at up to ~1% onto damp skin, then seal with moisturiser — treat it like hyaluronic acid. It's well tolerated, plays nicely with every other active, and is especially useful for dry, mature, sensitive or barrier-compromised skin, AM and PM.
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