Rashes are tricky. That looks like it could be from heat, or if could be from a virus. My kids get a similar rash on their bellies and back when they get sick. Even regular colds can cause a viral rash. If it's not bothering him and he seems healthy, there's not much to do but keep an eye on it.
Mama of 4 beautiful little ones
Unless someone like you cares a whole awful lot, nothing is going to get better, it's not.