Why does this hurt the balls?

There has to be a technically reason for this. My husband can’t explain it other than saying “it just hurts”.

While in the shower, and pointing the shower head at him. Back story: Our shower head detaches, and the thing that it attaches to is broken. We have to shower together so I can shave. It just makes more sense.
So, I pointed the water head at his penis and balls area…he whined that it hurt and said his balls are sensitive.
Why would water pointed onto your balls hurt? Why are they so sensitive? Is my husband just being a baby?