TRESemmé keratin shampoo allegedly causes hair loss and other problems, according to a recent class action lawsuit. Plaintiff Emily Castillo says Unilever misrepresents its TRESemmé Keratin Smooth Color Shampoo as safe and effective. In contrast with these representations, the TRESemmé hair products allegedly cause hair loss and scalp irritation. Keratin is a type of protein found in the hair, skin and nails, according to Healthline. Because keratin is the building block of hair, many products include keratin ingredients with claims the protein can help improve the strength and appearance of hair. Professional keratin treatments are popular at salons, but keratin supplements and hair-care