Bulldogs World

My puppy has started developing these pigmented spots (photo below) all over his belly! Initially, I noticed it was concentrated in the area where he tends to sit on his urine, but when I took him to the beach this past weekend, his entire belly has become littered with them! Moreover, the area on his inner legs and arms have become discoloured!

Is this unhealthy and an indication of something bigger? Also, can it be reversed?

Please help!