Many cuke varieties have bitter skins,that's well known, the ones that are Cucumis sativus,true cukes, which is why I plant a variety of cukes, known to not have bitter skins,such as Miniature White and friends.
And why I prefer the Armenian cukes,used as cukes, but are really Cucumis melo,that's right, a melon. And no need to ever peel them and there are several kinds.
https://www.google.com/search?q=Arme...&bih=788&dpr=1
https://www.google.com/search?hl=en&...k1.b8_UOS2itAU
Carolyn