Lots of supermarket brands of hair products contain silicones as they make the hair easier to comb, increase the fullness of the hair, or make the hair shiny and smooth. They create a short term illusion that the quality of our hair has improved.
However, when used over time, silicone-based hair products coat the hair shaft and seal out moisture, possibly clogging the hair follicles. So what happens is that hair can become flat and greasy with build-up or dry and straw like with a lack of moisture.
Silicones are particularly bad for colored or permed hair as the hair will appear fizzy with excessive coating.