4mo boy has red irregular shapes rashes on face at night, disappear within one hour or so. rashes not above skin.don't see at day time. what are they?

They sound like they: could be hives, which may be a reaction to something in his environment or something he is eating (if he is on solid foods). Has he been recently weaned from breast milk? Have him seen by his pediatrician, or if the rash isn't there at all during the day, try to take a photo and show it to his doctor. If you are on HealthTap Prime, you could do a consult with one of us.