I’m quite sure that mosquitoes are attracted to some people much more than to others. I’m quite never bitten by mosquitoes, and even less or not at all if there is some other meal (someone else) around. When I used to hike with friends or in similar situation, the difference were obvious. Also, an ex used to be always bitten when we were together (and not me). When one of our close friends was with us, the mosquitoes attacked him instead of my ex. And the three of us were thin, so it wasn’t related to that.
And the diference has nothing to do with the skin surface.In this case, the difference between two persons would be limited. But the difference is actually much more important than that. For instance, I remember one night I spent with my ex with open windows. On the morning, she had more than 40 mosquitoes bites and I had none.
I read somewhere it was related to skin acidity, but I don’t know if it’s true.