My bf, when he goes in the cold, comes back in & his exposed skin is bright red & itchy. What could it be caused by? Anything cold: water, ice, temperature. Should he go to a dermatologist or someone else?

Cold urticaria. is a condition similar to what you describe, but yes i would see dermatologist. If it is cold urticaria, it is a histamine reaction to any cold exposure on the skin.
It's . It's possible that your friend is experiencing hives that are induced by exposure to the cold, something called cold urticaria or"cold hives". The first line of treatment is avoiding exposure as much as possible, but he should also see his dermatologist to confirm the that this is the correct diagnosis and discuss other treatment options.