Niacinamide
The B3 vitamin that actually has receipts: fixes your barrier, dims oil, fades dark spots.
Grounded in the research on Nicotinamide (Wikipedia)
What it actually is
Niacinamide is nicotinamide, the amide form of vitamin B3 (niacin). Same molecule on your serum bottle and in your bloodstream. It's water-soluble, your body makes it from tryptophan, and topically it's one of the few skincare actives with real peer-reviewed backing, not just vibes. Don't confuse it with niacin (nicotinic acid) which is the one that gives you the flushing reaction.
The mechanism: it makes NAD+
In your cells niacinamide is the precursor to NAD+ and NADP+, the coenzymes that run energy metabolism and DNA repair. Topically that means more cellular fuel, plus it ramps up ceramide and free fatty acid synthesis in the stratum corneum. Translation: it rebuilds your skin barrier so you lose less water and react to less. This is the whole reason it works.