I bought a shoulder strap for my guitar, it is some type of material, but it is not leather. After my playing for about a half hour today, I noticed that an area of my back is red and bruised. I am not asking for medical advice, I am just wondering if anyone has had similar experiences with guitar straps and if so, what to do about it? I bought it a few months ago so I don't think I can return it.

I appreciate all of your advice.

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Are you placing it onto exposed skin?

Also, this is completely unrelated and just for curiosity, have you been in a fight because unless you have a heavy as hell guitar it shouldnt do that. Wear like, a hoodie between the strap and your shoulder.
Before i bought a proper padded leather strap i had a shitty strap which came with my first guitar that sort of irritated my skin after a while but never BRUISED my skin. That doesn't really make much sense how it could bruise.
Yeah. It doesnt matter if its leather or not either - I have a clip-lok strap and its fine.

Never been bruised by a strap.

Unless you whip yourself with it???
Are you sure it's bruised, cause maybe you sweated and the dye came out of the strap and stained your skin.