My husband has multiple light red spots on his back, not itchy, not raised. we noticed it after he showered. should we be concerned?

Hemangioma?: Probably Capillary hemangioma. Sometimes goes away by itself. See your doctor if it changes.

Concerned enough: You should be concerned enough to have your doctor take a look at it, diagnose and treat it if necessary. Off hand, it's unlikely to be something serious, but why be concerned unnecessarily? On the other hand, why ignore something that you should be concerned about? Again, it's best to know for sure what the rash is.