Biotin shampoo is recommended for thinning hair as biotin is a crucial nutrient that can decrease hair thinning and breakage. While biotin supplements can help, washing hair regularly with a biotin shampoo and conditioner provides the best results for improving thinning hair. It is important to choose an all-natural biotin shampoo without harmful chemicals like sulfates, parabens, and silicones that can strip the hair of nutrients and prevent it from getting thicker and fuller.