What can causes blotches on your face?

Lots of things can cause blotches on your face, it can be heat rash, allergies, excema, dermatitis, or just dry skin. If it is all the time, I would recommend seeing a dr or a dermatologist. If it's just sometimes, see if you can remember something similar happening around each time it happens, and then see if you can eliminate it. Or if it's dry skin, just use moisturiser.