N acetyl cysteine, often shortened to NAC, is a modified form of the amino acid cysteine that the body uses to build glutathione, one of its most important internal antioxidants.
Applied to skin, laboratory research has found that topical NAC can speed up wound healing through a specific cell signaling pathway, and separate human research found that topical NAC combined with the plant compound genistein helped prevent some of the cell signaling changes that UV light triggers and that lead to photoaging over time.
Other clinical research has found that topical NAC can help restore skin barrier function in both healthy volunteers and people with atopic dermatitis.
N-Acetyl Cysteine References
Topical N-Acetylcysteine Accelerates Wound Healing In Vitro and In Vivo via the PKC/Stat3 Pathway, 2014
Topical N-Acetyl Cysteine and Genistein Prevent Ultraviolet Light Induced Signaling That Leads to Photoaging in Human Skin In Vivo, Journal of Investigative Dermatology, 2003
Our team reviews ingredient research and uses up-to-date evidence to rate ingredients based on the categories below.
Best
Ingredients with the most rigorous and convincing evidence. These are the standouts backed by consistent findings across independent, peer reviewed clinical research.. When we call an ingredient Best, it has earned that distinction through genuine, reproducible proof that it improves skin.
Good
Reliable, well tolerated ingredients that do their job without complaint. They may not carry the headline benefits of a Best rated active, but they hydrate, stabilize a formula, or support the ingredients around them in ways that make a real difference in how a product performs and feels.
Average
Ingredients that are perfectly safe and serve a clear function, typically as an emollient, thickener, or filler, but do not offer any meaningful skin benefit beyond that basic job. Not a red flag, just not a reason to choose one product over another.
Bad/Worst
Ingredients with documented potential to irritate skin, disrupt the barrier, or trigger sensitization in some users, often synthetic fragrance, drying forms of alcohol, or certain essential oils. Not automatically a dealbreaker for every skin type, but worth knowing about before you commit to a product.
