As we age, our hair changes, and thinning is just one of the possible shifts. The MIT scientists who created Living Proof turned their attention to aging hair and developed Living Proof Timeless Shampoo, $28, to reverse and fight all signs of hair aging. In addition to Living Proof's signature ingredient (OFPMA -- which balances moisture and repels dirt and oil), this shampoo contains amino acids to strengthen strands and ceramide-like lipids to seal hair cuticles, which helps prevents damage and makes hair look fuller and healthier.

Hairmax Density Shampoo, $20, balances scalp oils and deeply cleans hair, but it's the special blend of DHT blockers, antioxidants and botanicals that makes this shampoo special. DHT (dihydrotestosterone) is a hormonal byproduct that shrinks hair follicles and contributes to baldness and hair loss, and there's scientific evidence that shows that topical treatments -- like the ingredients in this shampoo -- may stop DHT before it does damage.

Coloring your hair may make it appear thicker in the short term, but it can contribute to long-term damage and thinning. Alterna Caviar Anti-Aging BodyBuilding Volume Shampoo, $32, addresses this concern by preserving color while simultaneously moisturizing and repairing hair with caviar extract, marine botanicals, keratin, panthenol and biotin.

If you think pollution or excessive oil might be at the heart of your hair problems, Paul Mitchell Lemon Sage Thickening Shampoo, $17, may be your ideal thinning hair shampoo. It contains tea tree oil to detoxify and cleanse -- it's like an astringent for your scalp -- as well as panthenol to reinforce each hair strand. And the lemon and sage scent is seriously invigorating.

Scalp buildup -- think oil, hair products and dirt -- can contribute to thinning hair. And Bumble and Bumble Full Potential Hair Preserving Shampoo, $31, directly addresses these causes by exfoliating the scalp. It contains menthol, which tingles while it cleans, as well as creatine to reinforce hair strands and UV absorbers to protect the scalp and hair from sun damage.