We were all impacted by Kaneki's hair color change after Jason's unbearable torture. But how do you explain the sudden white hair? And more importantly, is there a serious theory explaining why did Kaneki's hair turned white?
The first theory is that Kaneki experienced the "Marie Antoinette" syndrome which, after very intense stress, leads to hair discoloration. The second theory, which is more official and seems to be the most serious, comes from Tokyo Ghoul RE where Touka asks Kaneki why his hair color changes so much and Kaneki explains that it is due to variations in the level of Rc cells in his blood.
But these reasons giving you these answers without any explanations would be very bad manners, so let's focus deeper and discover together the real reason why kanekis hair turned white!
Why does Kaneki's hair turn white
According to Sui Ishida, the genius mangaka of Tokyo Ghoul, he loves and has a real passion for the human body and how to play with it to tell his story. This is reflected in his work by the existence of ghouls which he explained by the creating the terms RC cells and the mysterious Kakuhou organ.
Since most living things catch diseases through their environment, Sui Ishida uses fundamental concepts of human anatomy and combines them with medical theories to create his own diseases and incorporating them in the Tokyo Ghoul plot (e.g. the disease of over-secretion of Rc cells).
This means that, in general, almost all physical and biological changes that occur in the Tokyo Ghoul universe can be explained on the basis of scientific and medical concepts.
As for our question about Kaneki's hair change of color, to date, Sui Ishida has not officially giving us the reason for this event, although he has put forward some theories...
1. Marie-Antoinette Syndrome
A: Before Stress - B: After Stress
The story goes that the hair of Queen Marie-Antoinette of France became white after her capture during the French Revolution. Witnesses have stated that Antoinette's hair suddenly turned white due to the extreme stress she experienced during her capture and eventual happening death.
Although there is no factual evidence other than the witnesses' sayings, Marie Antoinette Syndrome has gained popularity as a visual representation of extreme stress.
For example, since Kaneki was tortured relentlessly, two or three times a day for more than ten days, it is generally explained that the stress related to this torture could be the reason for his color change.
Since the existence of Marie Antoinette Syndrome has not been scientifically proven, one theory is that due to the stress experienced during the torture, a variant of "alopecia areata diffusa" was activated which affected the black colored hair, leaving only white hair.
2. RC Cells Over-secretion
The most official theory comes from Tokyo Ghoul RE: Touka asked Kaneki about his ever-changing hair and he replied that the CGC thought it was due to his sudden change in Rc-cell levels. The increase in his Rc levels probably affected his melanin production, causing the discoloration.
This would indeed explain why his hair was white when he fought Jason because at that time, Kaneki totally accepted his ghoulish side, increasing his RC cell count.
Moreover, colors play a major role in Tokyo Ghoul. In Eastern cultures, black hair color is used to signify health, prosperity and intelligence, while in Japan, black symbolizes the color of mystery and night. White, on the other hand, symbolizes death, sadness and, above all, tragedy.
Why does kaneki have white hair?
As explained before, there is no real answer to this question yet as the author didn't divulgate any further information on that subject.
A good answer that we could give you is that the sudden change of hair color could be the decision of Kaneki Ken to give up his humanity.
Indeed, just before his color happen to change of color, Kaneki's spirit was tormented by Rize that explained him that we should no longer think as a humain but as a Ghoul in order to survive.
In the end, Kaneki resigned himself and let go his new true nature and, therefore, acknowledging his new identity as a Ghoul.