The skin barrier is the outermost layer of skin, a wall of flattened cells sealed with natural lipids that holds moisture in and keeps irritants, allergens and microbes out. A healthy barrier looks calm and tolerates products well.
Over cleansing, over exfoliating and starting too many actives at once strip the lipid seal, producing stinging, redness and breakouts that mimic other conditions. Repair is simple but slow: gentle cleanser, regular moisturiser and pausing actives. Eczema and dermatitis involve barrier weakness and benefit from medical treatment during flares.