Hello, 2TF, thanks for the like.
As far as I know, Jennifer Lien developed an allergy to the glue that held her elf-like ears that's why TPTB decided to change the wig and give her long hair. Which is funny because her real hair was long in the first place, anyway.
I don't know, though if there ever was an in-story explanation for the hair change. I don't recall one.
As for me, I prefer Kes with short hair. Not at the beginning of the show, though: there's something wrong with that wig, especially in PARALLAX, which I can't really pinpoint what it is - but thank God, it had changed by the end of the first few episodes, and for the better, IMHO.
I guess I prefer her with short hair because for me that long hair was somehow not in accordance with the innocence and (to a certain extent) endearing naiveté that Kes had stood for during most of the time of the show.
However, watching the series for the 34th time, I must say I've got used to her long hair as well and I think it suits her just fine. Having seen the show so many times also means that whenever I see her with that long hair for the first time in BEFORE AND AFTER, I know that her time in the show is nearing to the end and in this sense her long hair has become the symbol of a forthcoming unfortunate event for me.
I've never thought about what her long hair looks like in profile but now that you mention it, I think it looks very pretty (she's definitely much more appealing in the above wallpaper than Seven ...). I know that a lot of people don't like THE GIFT, and I can't say I'm not heartbroken at least a little every time I see her leave the show. However, over the years I've got so used to it that I think THE GIFT was a beautiful way of making her exit the show. At least she wasn't killed off and gave Voyager a wonderful gift. In addition, the episode also suggested that she'd find a better way of existence and that message was also reassuring.
It's a pity FURY ruined all that.
Kes will soon come in one of my pictures in the series of wallpapers which you liked with B'Elanna. However, for today here's Janeway and Chakotay for all the J/C shippers in my next post.
That's right. She got allergic problems and therefore they decidet that she could have long hair instead so she didn't have to wear the Ocampa ears.
I did read somewhere that her long hair was a wig too but I haven't got it confirmed in any official article.
Her change of hairstyle was never explained in any way in the series. When I first watched "Before And After" I thought that her long hair was because of the scenario in that episode. Therefore I was surprised when she had long hair in the following episodes too.
However, I like her better in short hair because it personifies the character and ade her unique in some way. With the long hair, she looks just like any Starfleet character, although she did look great in long hair too.
Her early hairstyle in the first Voyager episodes were great too but it became even better in "The Cloud" in which it had changed to the more recognizible Kes style.
As for "The Gift", no I can't stand that episode.
There is only one Star Trek episode which is worse.
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And it's one thing I've never found anyone similar to him in real life. What is more amazing is that I've never found anyone like him in the realm of fiction, either! 
