Formaldehyde donor preservatives are under debate because formaldehyde at high concentration is known to the public as a toxic substance to humans and the environment, inducing mutation in living organisms. Chemical methods, such as using acetylacetone(Nash reagent), are commonly used to determine total formaldehyde concentration in cosmetics. However, these methods will perturb the equilibrium between formaldehyde and formaldehyde donor. A new method, based on C-13 NMR, not perturbing the equilibrium and more suitable for formaldehyde measurement, is reviewed. This review describes the background, distinction, and applications of formaldehyde and formaldehyde donor in cosmetics.