Synthetic, formaldehyde-releasing preservative that has mixed research on its potential to aggravate skin. Despite its connection to formaldehyde, the Cosmetic Ingredient Review Board has confirmed the safety of this preservative in three separate reviews, each spaced several years apart.
References for this information:
The Personal Care Products Council (the Council). DMDM Hydantoin. [Internet]. 2015 [cited 2015 July]. Available from: http://www.cosmeticsinfo.org/ingredient/dmdmhydantoin