L’Oréal Total Repair Serum is a popular product that helps make damaged hair softer and easier to manage. Most people use it without any problems, but some might experience mild side effects like irritation, dryness, or sensitivity because of certain ingredients. These reactions are rare and usually depend on your skin or scalp. It’s a good idea to test a small amount first, and if you notice any irritation, stop using it and talk to a doctor if needed.