Loss of color on top of my hand?

i have a spot that started as a little white spot on my hand about 4 years ago. over the years it has grown, not huge, but maybe the diamater of a dime. in the winter time, i dont have issues with it, but now that summer is here and i am outside, it seems to get burned on the outer edge. i was out in the sun golfing on tuesday, and on wendesday it was red on the outer part and has tiny bumps, it will itch sometimes. Also, on my left arm, i can see alot of red dots after being in the sun. Anyone have any idea what this is? I know its a loss of pigment, but could it be life threatning? thanks