Board Thread:Naruto Discussions/@comment-26431570-20190526171926/@comment-39559503-20190526214334

For Naruto - I have a feeling it's because he grew up in the womb with Kurama's influence nearby, which rubbed off on him while he was developing. Especially because he had the whiskers before he became Kurama's jinchuuriki. Boruto and Himawari are a bit foggier, maybe they only have two whiskers because they didn't develop with Kurama right next to them, but their only exposure being from Naruto's DNA.

But that doesn't explain why Tsunade, a descendant of Mito's, has no whiskers. So any guess is as good as mine.