I realize that sometimes hair gets dirty... but there's no way it gets dirty enough to require industrial strength chemicals to clean it. However, according to an article on the Davide Suzuki Foundation website chemicals including carcinogens and pesticides are all too common in personal care products.

The article gives 12 ingredients to watch out for, including
BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene. BHA and BHT are used mainly in moisturizers and makeup as antioxidants and preservatives. BHA has been classified as a human carcinogen and studies suggest that BHT could be toxic to the skin, liver and immune system.

For more information on harmful ingredients in personal care products click here.