the increased sun exposure induces tanning which could be the cause of darkness on your hands, also dullness could be from the tanning in combination with nutritional causes due to improper diet which could have been causes by your traveling schedule. The problem can be managed with peels along with lightening creams and tablets. And to prevent further aggravation proper sun protection will be very important. Kindly get it examined and assessed by a qualified dermatologist in person for a proper and thorough evaluation and starting the right treatment. Hope this was helpful.