New Lawsuit Targets Unilever's TRESemmé Over DMDM Hair Loss Claims

Plaintiffs last week filed a product liability lawsuit in New Jersey federal court against Unilever's Conopco division, claiming that TRESemmé hair products containing the preservative DMDM hydantoin lead to hair loss. The suit is the latest in a series of legal actions targeting the ingredient.

DMDM hydantoin has been used globally for decades as an antimicrobial preservative in cosmetics. It works by releasing trace amounts of formaldehyde over a product's shelf life to prevent microbial growth. However, the concentrations involved are extremely low—typically 0.0005% to 0.6% in shampoos—and are regulated by authorities such as the European Union, which permits up to 0.6%.

This contrasts sharply with formaldehyde used in professional hair-straightening treatments, which can contain much higher levels. In a 2011 warning letter to Brazilian Blowout, the FDA found methylene glycol concentrations ranging from 8.7% to 10.4% in samples, far exceeding the trace amounts released by DMDM in shampoos.

Previous court rulings have repeatedly rejected claims that DMDM causes hair loss, citing lack of scientific evidence. The new lawsuit now faces an uphill battle, as the science and legal precedents continue to challenge the alleged link between the preservative and consumer harm.