In a move that should make fans of the original movies very happy, the new Ghostbusters features a big, climatic fight scene in which the four Ghostbusters team up against chaos-causing ghosts. That's no big surprise, considering that most big summer movies consist of a huge, action-packed finale scene, but what will come as a surprise is the fact that (spoiler alert!) Erin (Kristen Wiig) and Abby (Melissa McCarthy) undergo a pretty big physical change after they make it out alive of the ghost-filled vortex. If you're wondering why the Ghostbusters' hair turns white at the end of the movie, trust me — you're not alone.
There may be no one actually scientific reason (this is a movie about bustin' ghosts, after all) for the Ghostbusters' hair changing color after this big finale, but there are a few possible explanations that make some sense. First of all, there's the fact that by going into the vortex, Erin and Abby basically traveled through time, and so their white hair is representative of their "older" age. There's also the option that the white hair is not about time travel of any sort, but simply the fact that Erin and Abby were bound to be changed in some way, considering that they managed to pass through to the other side, the home of the ghosts, and come back. The fact that they accomplished this without dying is pretty impressive, so it makes sense that they wouldn't come back from the vortex without a single issue.
Still, it's a bit surprising that Abby and Erin's faces didn't show any sign of aging, only their hair. Wouldn't it make more sense for that to be affected, too? Yet it's totally understandable that the movie didn't go that route, as it'd be pretty inconvenient to make those two Ghostbusters look several decades over for the rest of the movie. Giving them white hair is a lot easier, and, as Holtzmann and Patty's reactions in the scene showed, totally funny enough to carry the scene.