Hard to tell from the picture, but these look like so-called "liver spots," that have nothing to do with the liver but appear on sun-exposed areas if there's a genetic background for them. You can't stop them from coming, but minimizing sun exposure helps and you can have them frozen or lasered off quite easily. Bleaching creams may be worth a try too. As your doctor.
Take care.
Dr. Rockoff
try this link hopefully the pictures will show
http://img506.imageshack.us/img506/1557/dscf0007960x720lf1.jpg
http://img455.imageshack.us/img455/7102/dscf0010960x720pu9.jpg
Do liver spots darken when you sweat or in hot weather because the spots on my arms get really dark in those conditions.