What is this???

So today I noticed that my sons face has been really blotchy and it looks like a rash but I don’t know what it would be he hasn’t eaten anything out of the ordinary and I am kind of worried because that’s my first child and I’ve never seen this before! I was thinking it was maybe when his milk drips down or because he’s drooling a lot. Could he just have sensitive skin? I’m not the kind of person to take him to the doctor unless I believe there’s a reason. He gets stuff like this on his chest neck and body sometimes but it’s rare. His face started today