Hate my family touching my stuff

I have a thing where I HATE it when my family touches my stuff. But it’s only conditional where if it’s something new I bought and they touch it then I would feel like they made it dirty. The thing is, I would feel really upset and angry over it. Sometimes I would even throw the object they touched away just because of how upset I get over it and I would stay upset for a day or two until I feel like the object isn’t dirty anymore. During the time I’m upset, I would even hit myself to calm myself down, but it doesn’t work. This also applies to people I don’t like. So basically my sister is married and my brother in law used to live with us and they share the same bed. Sometimes I would hang out in their room because I wanna hang out with my sister, but when my sister tells me to sit on their bed, I would deject it so much just because my brother in law sleeps in the bed. There are also times when they touch my arm or clothes and I would immediately go and wash the areas they touched over and over again and I would just get so upset. This only applies to my family and a few of the people I don’t like, but I don’t react the same when it comes to my friends. I don’t know why I act like this but it gets so frustrating sometimes.