Why? Because you want to avoid products that have paraben, sulfates, and silicone. Parabens are preservatives that are known to be an endocrine disruptor and can mess with the levels of estrogen in the human body. Sulfates are also a preservative, but work by emulsifying the product aka they are what make it bubly. Silicones are not exactly bad, but silicones do coat the hair in a slick substance. This prevents hair from absorbing moisture, so deep conditioning hair with a product with silicone in it defeats the purpose because the moisture will never hit your actual hair. Bianca Renee Today has a great video on selecting products.