NAD+, azelaic acid, and anti-aging serums: what holds up?

What did @kbeauty_code actually say?

The creator, identifying as a Korean pharmacist, rated five skincare products on a scale of 1 to 10, with the main argument being that topical NMN is superior to topical NAD+ for anti-aging. They gave Anua Azelaic Acid Serum a 4/10, calling it good for redness but "not truly effective anti-aging." Numbuzin No.9 Essence got a 7/10 for containing "NADs which increases cell repair and slows down aging." The clear winner in their ranking was a Story NMN Intensive Serum at 10/10, because NMN is a "pre-corner" (precursor) of NAD+, and therefore "more effective anti-aging and cell regeneration." BioDance collagen serum scored 3/10 because collagen "doesn't absorb very well," and a BT retinoid product got 6/10 with a note that it improves fine lines but may not suit all skin types.

Does the science back this up?

Partially, but the 10/10 for topical NMN is not supported by clinical evidence in humans. The logic is sound on paper but the leap to a perfect score is not. NAD+ does decline with age, and NMN is indeed a precursor to NAD+. The problem is that topical delivery of NMN into skin cells has not been validated by robust human clinical trials.

The NAD+ biology is real. Yoshino et al. (2018, Cell Metabolism) confirmed that NMN supplementation in mice improved metabolic function by raising NAD+ levels. But oral supplementation is not topical application. Skin has a lipid barrier that is selective about what it lets through. A molecule being biologically active does not mean it survives on your skin surface and penetrates to where it needs to work.

The collagen absorption point is well-supported. Collagen molecules are large (roughly 300 kDa), and transdermal absorption at that molecular weight is essentially zero. Bos and Meinardi (2000, Experimental Dermatology) established that molecules above 500 Da penetrate skin poorly. Collagen in a serum is mostly a surface moisturizer. The creator gets credit for that one.

What did they get wrong (or right)?

Right: collagen serums are moisturizers, not anti-aging treatments at the cellular level. Right: azelaic acid is primarily a skin-calming ingredient, not an anti-aging heavy hitter. Right: retinoids improve fine lines, and they do have tolerability issues for sensitive skin types. Those are fair assessments with real backing.

Wrong, or at least unverifiable: rating topical NMN a perfect 10/10. There are no peer-reviewed randomized controlled trials in humans demonstrating that topical NMN penetrates the skin barrier and meaningfully raises intracellular NAD+ levels in keratinocytes or dermal fibroblasts. The precursor logic is reasonable for oral or injectable NMN, but applying it to a serum and giving it a perfect score misleads viewers into thinking the science is settled when it is not.

Also worth noting: NAD+ itself has poor transdermal absorption too. Giving Numbuzin a 7/10 for containing NAD+ while the underlying delivery problem exists for both products makes the scoring inconsistent.

What should you actually know?

If you are interested in NAD+ biology for skin aging, the honest answer is that oral NMN supplementation has more clinical support than topical application. Massudi et al. (2012, PLOS ONE) confirmed age-related NAD+ decline in human tissue, and research into NMN as an oral supplement is ongoing with some promising human data. Topical formats are speculative at this stage.

For ingredients with actual topical anti-aging evidence, retinoids remain the gold standard. Varani et al. (2000, Journal of Investigative Dermatology) showed retinol increases collagen production in aged skin. Peptides like GHK-Cu have some skin-level evidence for wound healing and collagen stimulation. Skin-penetrating peptides are a different structural class than large proteins, which is why they behave differently than topical collagen.

The creator's framing, that a higher rating means more proven anti-aging efficacy, sets up a false hierarchy. Azelaic acid is not trying to be an anti-aging compound. It treats hyperpigmentation and redness. Judging it low for not doing what it was never designed to do is like rating a sunscreen poorly for not being a moisturizer.

Bottom line

The creator gets the basic NAD+ biology right and makes defensible points about collagen absorption. But a 10/10 for any topical NMN serum is premature given current evidence. Viewers should treat NAD+ and NMN serums as interesting early-stage science, not proven treatments, and should not expect the same results as oral supplementation protocols studied in clinical settings.