I am trying to keep my hair really healthy, been doing very well with taking the prenatal vitamins…

I am trying to keep my hair really healthy, been doing very well with taking the prenatal vitamins and conditioning and such. I was wondering though, I've heard there is an ingredient in shampoo and conditioner that is suppose to be avoided cause it can damage your hair. Does anyone know what it is that is best to be avoided and what shampoos and conditioners are best to use?