Exposure to UV rays can cause an increase in melanin production and this can lead to tanning and dull skin. The other common causes of dull and dark...Exposure to UV rays can cause an increase in melanin production and this can lead to tanning and dull skin. The other common causes of dull and dark skin are dehydration, stress, thyroid dysfunction, hyperandrogenism, lack in vitamins, minerals, etc. www.skindecor.in/Show more