Couldn't find any answer to this, and I noticed that I was developing some self destructive behaviours lately and I am not going to analyse myself but I am just curious, so anyone know the answer?
While it might not necessarily itself be a mental illness, self-destructive behavior is a result of a few different mental illnesses (addiction, BPD, depression, etc.)
The natural instinct for people and all animals is to survive and to avoid pain. So when someone inflicts pain or damage on themselves (except for those who use pain for erotic purposes) it's unnatural. In my opinion it indicates something isn't right in that persons thoughts and/or emotions. Does that sound like mental health? The opposite of health is illness. So is it technically mental illness? I don't know. I never studied the DSM and I've never had an inclination toward self destruction.
I agree with this, and Blootsvoets also raised a good point. I'm bipolar (type II) and self-destruction is part of both mania and depression. It doesn't have to be cutting, burning, or otherwise inflicting pain to oneself, but self-destruction can be negative thoughts about oneself too. It's a way of breaking yourself down, ultimately leaving you feeling worthless, which can then very easily lead to severe depression. So though I doubt that self-destruction in itself is a mental illness, as Killswitch has suggested, there are a few mental illnesses, of which self-destruction is a symptom. My advice to you is to speak to a mental health professional, who will assess the situation and tell you whether or not you actually suffer from a mental illness. (*hug*)
Definitely talk to someone. No self destruction like cutting, pulling out hair and stuff isn't a mental illness in and of itself but, it is an indication of some serious issues going on in your mind and, you need to figure out what those are and, how to deal with them in a healthy way. That's where a therapist comes in. Don't try to learn and do it alone, few ever succeed at that. But whatever you do, find a way to end the self destruction before it gets worse.