What is this itchy red bump?

For years I've randomly had single red bumps appear on my face, stomach, arms, neck, ect. They usually only come one at a time. I've noticed they come usually when I'm stressed, hot, or sweating. But sometimes they come for no reason at all! A friend at work has the same problem, and I've noticed other people with this too. They look like mosquito bites, and if I don't scratch it it usually goes away in a/b an hour. I think it's a form of hives- does anyone know more details? Or does this happen to anyone else?