It could be said that a certain editorial change to the rulebook is splitting hairs, but it actually only clarifies existing rules.
An editorial change was made to the 2020 NFL rulebook with the new text in bold at Rule 3-2-6:
Touching the Ball refers to any contact with the ball. There is no distinction between a player touching the ball with his hands, or with any other part of his body, including his hair, except as specifically provided for.
A player’s hair is just as much in play as the rest of his body, and it is even legal to tackle a runner by the hair or a handful can be called a holding penalty. So, the added text above is nothing really new, but it underscores that a player whose hair touches the ball is not ignored as incidental.
Therefore, a punt that brushes through the flowing locks of a receiver is considered to be a live ball. A fumble that only touches the hair of a player with a foot out of bounds is a dead ball.
The casebook already has a distinction that a player can be down by contact if a defender only touches the hair of a ball carrier on the ground. That same casebook entry also addresses if the defender only touches the runner’s towel in his belt while on the ground. (It is not down by contact.)