Does sun exposure cause skin rashes?

Sometimes I have to go in sunlight during my work. I am suffering from skin rash behind my neck. I found whitish spots behind neck. I feel itchy. I always keep myself clean. What should I do?

 

First of all protect that area from strong sunlight by wearing something which will prevent sun exposure eg. by A, B, C method:
A = AWAY, Stay away from the sun in the middle of the day (between 10 AM & 3 PM)
B = BLOCK, Use SPF15 or higher sunscreen.
C = COVER UP, Wear a shirt and a hat.
You can apply a mid-potency topical cortico-steroid cream (eg. Betnovate cream) twice a day for about a week. A systemic anti-histamine (eg. Allegra-180 one tab/day) can also be used to prevent itching.
As for your white spots - contact a dermatologist in your area so that the possibility of vitiligo (leucoderma) is excluded.