They say that parabens are bad. They are used to keep your stuff from going bad. There was one research paper that connected parabens with breast cancer and they suddenly got a bad rep. If you use them and you're itchy afterwards, then you are allergic and you should avoid them
Sulfates can dry out whatever they are in. They can dry out out your skin and hair. Thing is that they are cheap to use, that is why they are in a lot of cosmetics. The list of sulfates is very long. So you can avoid them but it then you have to check the ingredients of everything. And it is not guaranteed to dry out. Some people do not react to them and some people do. Imo you do not have to avoid all of these unless you notice that your shampoo or cream noticeably dry you out and that was not the case before you used it
Silicones lay a layer around your hair. It makes your hair smoother. Looks amazing but it also weights it down. If you don't have a lot of hair, this is not what you need. And off course avoid it if you are allergic. As long as it does not sting, burns or itches after you applied it, that is not the case
You also have silicones in moisturizer. That is why some face creams make your skin smooth and velvet like
First thing is knowing if you are allergic. If you are not, it is not necessary to avoid them. If they are actually that bad for you they would not allow them to be used and sold. If you do want to avoid them, google what they are and read ingrediënt lists. And don't forget that things like drinking water, using oil as a hairmask once in a while and sleeping in a silk pillowcover or using a bonnet can also do wonders for your hair