How to tell what a newborn rash vs allergic reaction looks like?

Skin rashes: Skin rashes need to be looked at so we can give you a proper diagnosis. By saying allergic reaction, i assume you refer to skin rashes due to an allergic reaction. There are generally 2 types of skin rashes due to an allergic reaction, an immediate reaction causing hives and a late reaction causing dermatitis. The later may look like a newborn rash. They can be treated the same way.