Ectoin
In plain terms
A protective molecule that microbes make to survive extreme heat, salt, and dryness, used in skincare to hold water and shield the skin barrier. It is well tolerated, even on sensitive and inflamed skin.
What the evidence shows
Ectoine is an extremolyte, a small molecule that bacteria living in salt flats and hot springs produce to protect their proteins and membranes from stress. In skincare it works by binding a shell of water around itself, which hydrates and helps stabilize the skin barrier. The clinical record is unusually good for a newer active: a systematic review found topical ectoine up to seven percent very well tolerated in both adults and children over months of use, and controlled trials in atopic dermatitis and irritated skin found ectoine creams calmed inflammation with tolerance comparable to the anti-inflammatory creams they were tested against. Side effects are rare and mild, mostly a brief tingling or redness at the highest strengths. There is no hormone, cancer, or contamination concern attached to it, and because it is used at low levels and is well cleared, the safety picture is quiet. It is a gentle hydrator that suits reactive skin.
On the label
Listed as ectoine, usually in the hydrating or barrier-support part of a serum or moisturizer. It is gentle enough for sensitive and eczema-prone skin, and is often paired with other humectants rather than used on its own.