Board Thread:Boruto Discussions/@comment-25192437-20191112175648/@comment-4080775-20191113000506

Organic Dinosaur on Twitter explained it best, as she translates and such as she gets more information.

Naruto's illness is akin to an autoimmune diorder; Basically Naruto's body is becoming allergic to Kurama's chakra and as a result, his chakra pathway system is slowly closing itself in an attempt to stop the effects.

I can provide a link to the post, but only if an admin says I can. I'm not sure if I can post links or not.