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.