Redken Extreme Length Shampoo is a strengthening shampoo for damaged hair that gently cleanses hair and helps it grow longer and stronger over time. Formulated with biotin—a B vitamin known for its ability to promote healthy hair growth—Redken Extreme Length Shampoo helps to fortify the hair from root to tip, reducing breakage to help you reach your maximum hair length, of up to 6 inches of growth in one year.