is often used in conjunction with dimethicone. In fact, as a volatile silicone it quickly evaporates into the air after delivering nutrients to the skin and hair. It is also very inexpensive compared to organics compounds, which is why it is used.
On the whole, these siloxanes are not going to hurt you. However, it is important to understand that the chemical does not nourish or exfoliate skin the way vitamin A or vitamin E would do. Instead, the silicone often acts as a waterproofing agent, lubricates the skin, and offers a temporary shine. It does the same in hair products. In other words, it many give your skin or hair a smoothing effect and shiny appearance, but it is not actually "healing". It's purely a temporary fix. Also, since it does form a barrier on top of your skin, to help with hydration, it can also trap dirt and bacteria. It is important to use a good cleanser to wash your face each night when using a foundation or other cosmetic that contains silicones. This will also allow your skin to "breathe" overnight.
Should you use hair care products that contain silicones? They are safe, but if your hair is truly damaged, well, why pretend your hair is shiny and healthy when you can get the real thing with olive oil or coconut oil? If you decide you want to avoid Cyclopentasiloxane or other silicones, then there are manufacturers that now are using more organic ingredients. They may be a bit more expensive, but you may find it worth it.