What is this on my boyfriend's back?

This is my boyfriend's lower back, he said this rash type thing popped up today and it's very itchy. He's not sure where it came from because the past couple days he has just been relaxing at home and nothing touched it and he didn't use any new creams or anything on his back. He put some hydro... show more This is my boyfriend's lower back, he said this rash type thing popped up today and it's very itchy. He's not sure where it came from because the past couple days he has just been relaxing at home and nothing touched it and he didn't use any new creams or anything on his back.
He put some hydro cortizone on it and hasn't been touching it. We're just wondering, does anyone know what it is?
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