If seborrheic dermatitis is left untreated, can it possibly cause hair loss or small bald patches?

If you let it build hard plaques on the scalp and then you pick them off, it can cause hair loss. Just flaking scalp does not cause hair loss, though. An extreme example of seborrheic dermatitis is the disease called psoriasis, which does not cause hair loss unless the victim picks off the plaques on a chronic basis. My advice is to seek out a good dermatologist and get yourself looked at carefully.