The darkening of skin can be multiple causes like tanning, vitamin B12 deficiency, addisonian pigmentation, acanthosis nigricans, lichen planus pigmentosus, rhiel's melasnosis or several other causes. A proper assessment and examination will help ascertain the proper cause. For loss of glow & dullness - there are antioxidant therapies like glutathione , lasers for rejuvenation, PRP therpy for facial rejuvenation , peels, etc. Kojic acid alone is safe but less effective. The BEST cream would depend upon the cause. You can consult with me online as per your convenience and get further evaluation done or even better if you can drop by at my clinic for an unclose proper evaluation. Hope this was helpful.