dry skin or rash?

So I thought this little spot on my son's neck was dry skin as it is winter and very dry here. But the spot has spread, and he has similar dry spots on the front of his neck where his shirt collar is and small raised bumps on his arms and legs. I've been putting lotion on twice a day and that hasn't helped. haven't changed the laundry detergent. last time I introduced a new food was maybe the day before I first noticed the dry skin but he hasn't had it again, and no new foods since. ideas?