Formaldehyde is much more toxic than acetaldehyde. The difference seems mainly to be that formaldehyde is bifunctional due to its lack of steric inhibition in comparison to acetaldehyde, which is almost uniformly monofunctional. read more
A product of alcohol metabolism that is more toxic than alcohol itself, acetaldehyde is created when the alcohol in the liver is broken down by an enzyme called alcohol dehydrogenase. read more