I have a red zone in my face, like a rash, in my forearms.. sometimes is so red, and it have like little pimple... what could that be?

Rash: Rashes r difficult to diagnose without being seen since they can be cause by so many different things: acne, rosacea, lupus, contact dermatitis (make-up, shampoo, perfume, soap, jewelry, etc), medications. See pcp to evaluate the rash. Make list of any new skin care or laundry products & medications/ supplements to give doc.

Much more data neede: Could be a dermatologic condition, medication reaction if you are taking anything. Food allergy, etc. Questions need to be asked like onset, does it itch, what makes it worse or better, etc.. Start with your family doc and go from there.