You might be applying an incorrect dose
I wasn't thinking one night and decided I was going to literally douse my head in minoxidil. My eyes literally closed up from being so puffy and I broke out in hives everywhere. You must follow the recommended dose. I thought "meh, it's just Rogaine, what harm could it do?". Wrong. It's actually got pretty severe side effects if you overdo it. Plenty of people on Google have written about using too much in one application and what happened to them.