What vitamins can i take or what can i do for really dull skin, and brittle hair and nails, i also have dark under eye circles. thanks?

Normal nutrition: Young people rarely have vitamin deficiencies. Start with adequate sleep (allows time for your body to repair itself), a broad diet (protein, fruits, vegetables, and grains), and a lot of water. If still concerned, try a simple multi-vitamin. You can choose more expensive "programs, " but you probably can't do better than what nature offers.