FILE - This photo shows hair on a brush LOS ANGELES - A nationwide class-action lawsuit was filed against beauty conglomerate Unilever in November claiming that some of its Tresemmé products were allegedly causing hair loss."Plaintiff purchased the Products because of Unilever’s uniform false representation that the Products would smooth her hair and coat it with Keratin, a protein found naturally in hair," the lawsuit read. "The Products contain an ingredient or combination of ingredients that causes significant hair loss and/or scalp irritation upon proper application."One ingredient, a formaldehyde-releasing preservative DMDM hydantoin, was found in Tresemmé Keratin Hair Smoothing Shampoo and TRESemme Keratin Smooth Color Shampoo.RELATED.