For a thousand years, women have been using their hair to create elaborated hairstyles as head decoration, and has become a huge part of what defines beauty and seduction. "The naked woman" by Demson Morris, explains that no other part of the female body has shown as many cultural variations as the hair does; and now, more than ever, trends are multiplying. However, just as it is attractive, it is also a taboo for many religions from different cultures.
These multiple variations have been represented through thousands of paintings and sculptures by many artists from different periods and places, so they ended up mirroring the fashion of its time without even being aware of it.
Two examples: One of the most famous sculptures from the Stone Age the "Lespugue Venus" has hair represented with ivory from mammoth's bones. The hair is cut and styled at a level of detail that would amaze anyone. In "Venus of Willedorf", from the same age, we can see an enigmatic statuette with her head wrapped by a long plait that almost completely cover it.
We have to take into consideration that many artists only insinuate the hair of their models, because of its physical attributes that make it difficult to represent it accurately. A natural sized portrait has to show the length, the thickness and gloss of the hair, but it also must show the different colour-schemes that hair gets under specific lighting; which is practically impossible.
That's why the artist has no other option but to insinuate it through a mix of light-reflection, shadows and brightness; because every hairstyle has its own logic. Unless we're talking about hyper-realistic artists (who can be way more obsessive), realist artists are happy to achieve an indefinite, resembling effect.
When put in front of the work, the spectator is aware about the fact that the artists hasn't represented every single one of the almost hundreds of thousand of hair we have on our heads, but despite the results, the eye recognizes and understands what the artist has tried to represent.
Perhaps every painter, in the solidarity of the atelier, knows the fact that his metier is a never-ending task and it would be ridiculous to try achieve a mimetic representation of reality. After all and against any utopia, it is intuition what finally gets to the eye of the observer.