Any time you use any chemical on your hair, it is damaging to your hair. The more you apply the chemicals to it, then more you will damage it. The good thing is that your hair does grow back, so it doesn’t stay damaged the whole time.
However, it may become damaged because you are applying chemicals to it faster than the rate of your hair growth. In that case, you need to make sure that you are using permanent straighteners that do not have as much damaging chemicals in them.
There are other ways to straighten your hair without using chemicals, but they will still damage your hair. Straightening irons produce heat, but there are newer straighteners that cause less damage. These are the ones to use.