There are multiple causes for facial hyperpigmentation. Sun tan, overweight, pigmentation disorders like acanthosis nigricans or melasma, lichen planus pigmentosus, rhiel's melasnosis, nutritional deficiency etc are some conditions. The patches of pigmentation need to be examined and assessed to know the cause. Treating it without knowing the underlying cause will offer incomplete and temporary relief; also it will keep rebounding..... the alternate red and brown marks after the slap is because as the sites of finger contact with the face - the redness has set in... the skipped areas in the middle are the ones left brown.... meet a dermatologist directly for a proper evaluation of the condition. Hope this was helpful.