Ceramides

Ceramides 1, 3 and 6-II are the combination most researched, and it's what CeraVe built its range on. In practice you don't need to audit the numbers — a fragrance-free ceramide cream from a reputable brand will do the job.

Yes, and you should. They're what makes tolerating those ingredients possible. Ceramide moisturiser after the active, every time.

Two to four weeks, provided you've also stopped whatever was damaging it. The product alone won't outrun a harsh routine.

No. Oily skin damages its barrier just as easily, usually faster because of stronger cleansers and more exfoliation. Use a lighter texture, not less of them.