Weird way of masturbation. Safe?

I'm a 22 yo male and I think I have this weird or unique way to mastubate. I can masturbate easily without using my hand or any tools whatsoever. I just need to get a little horny and then put my penis in between my thighs. Then I kinda put a pressure my p and within few seconds, boom it loads off. My p size is relatively small I think, maybe that's why it could happen. And I have been doing this since 17-18 yo. I wonder if this is a problem or no. I also has this kinda skin desease in area between thighs (I dunno what it's called) and also on my butt. It's like a drying wound , sometimes it's a bit itchy and disturbing. I keep peeling it, and apparently it leaves dark marks to my skin. And the questions are: 1. Is this skin desease somehow caused by my weird way of masturbate? 2. Am I the only person that have this technique of masturbate? 3. Is this technique safe? Sorry for bad english