i have gone through your problem.
please mention about your age,are you exposed to sun very much,what medications you take.tanning
may be due to varios reason.
but your unexposed part tanning may be due to medications,internal disorders.
yet you take some general precautions
1.use good eg spf 30 or more sunscreen
2.physical sun protection in the form of hats,umbrella when you are in sun
3.sunglass for eye protection
hope this will help you.
you can send the above details and a photograph(2.5 mp carl ziess or equivalent) of the affected part to my mail firstname.lastname@example.org.
hope i will be able to solve the matter.
best of luck.