semen rash???

So I've been with my boyfriend for almost a year, he's my first and I was his and we've both been monogamous, but the past time we had sex he came on my chest and a few minutes later there was a rash consisting of red dots where the come had landed, it didn't itch or anything and he's came on me/in me before and nothing like this has ever happened, could it be something he ate or something?? I don't have any food allergies but idk