Holy Zohar text. Daily Zohar -227.

Tikkun 19 – 7

Binah is upper waters, represented by the letter H ה and Malchut is lower waters and is represented by the lower H ה of the YHVH name. They are connected with the letter V ו that represents Yessod.
The work of the Tzddik is to be like Yessod to connect upper and lower using the Vav ו as a pipe to channel down the light.

The sages say that the Holy One is strict with the Tzaddik even if it is like “single hair”. The term that the Zohar uses is “single hair” and it is here to describe the importance of a high level connection. When the Tzaddik is at the level of Yessod, the upper channels open to “pour” down the light. It is done through the “hair” of Arich Anpin.
The name Arich Anpin means “long face” and it is the energy that had started the process of creation.
It is the source that brought the light from the unknown and concealed light.
The hair has the aspect of light channeling to the world.

Women’s hair as Malchut, has the biggest capacity to draw light or any other energies. (That is why you almost never see a woman naturally bald). For the men, it is the hair from the eyebrows level and down that help in channeling the light.