Each testicle gets its blood supply in a slightly different way as the kidneys, there may be a slight variation in size but a big difference needs to be assessed, he should start with his doctor, it may be that the larger one has a hernia or varicocele or that the smaller one did not develop and has some problem with blood supply or other concern, worth getting it looked at, other sources would be a urologist
Well you know if you look at your hands one is smaller than the other.and if you look at your arms,legs feet,ears and alot of other body parts one is usually bigger than the other.So I would assume this is true for testicles as well.Of course cold doesnt help either
Completely normal. He should be checking his testicles once a month for testicular cancer. As long as he was born this way, it doesn't change in size or color, it isn't painful, and there are no bumps or nodules, he should be fine.
My breasts are different as well. Most women's are. Although sometimes its tough to tell which one is bigger. Either way, this is normal. Is there some reason why it bothers you? Other than you were worried something is medically wrong with him?