The surface and its barrier
The outermost film — and the first thing to check.
A barrier of cells and lipids whose job is to keep water in and irritants out. It is thin, repairable, and easily disrupted.
Tightness, stinging, flaking, flushing on contact, and products that were tolerated for years suddenly not being tolerated.
This is where daily care does most of its work — and where an unsuitable routine does most of its damage.
Almost nothing else works reliably on an irritated barrier. When this layer is unhappy, it is stabilised before anything is added.