A few years go in a college class, I overheard a conversation where one student asked another if her hair was naturally curly, or if it was a perm. The answer was that her hair use to be straight, but after getting one perm, it stayed curly ever since. I’m just curious how that’s possible.
Hair can go from straight to curly. Mine did. However, it was a strange result of timing, as far as I can tell.
I got my first perm at age 13. At around age 14 (OK, 4 days after my 14th birthday, TMI, TMI) I hit puberty. My hair was never straight again.
Sorry I don’t have a cite, but I believe that I’ve read that whether hair is curly or straight has to do with the shape of the follicle. This can be influenced by hormones (this can also result in more or less acne), but can’t be influenced by chemicals over the long term.
If someone has a cite I would love to read it.
Mine used to be curly, but then it went straight. No idea why.
Its not the shape of the follicle, but the pore.
Completely round pores give completely straight hair.
Oval pores produce wavy hair.
Slit shaped pores produces tight curls.
You know how pulling a length of ribbon tightly over a scissor blade will make it curly? Same phenomena.
So she probably either had the perm around puberty, or it went from straight to curly for unknown reasons I guess.
My hair went from straight to extremely curly in fourth grade after my mom gave me a home perm.
It’s been curly…VERY curly, since that day.
I’m the only person in my family with curly hair, and the hair starts curling as soon as it comes out.
I’ve had straighteners put in it several times but they never take for more than 48 hours.
I don’t know how it could have been hormones acting that fast! 
I know your hair can go from straght to curly, or the reverse, because of pregnancy.
Mine curled up not because of a perm, but because it had always been curly. Until I got a ‘layered’ cut and discovered blowdryers and mousse, the weight of my long hair, plus vigorous brushing, tended to make my hair straight.
The daughter of a friend of my mother’s friend (sounds like an urban legend I know but I can give names if required!) got toxic shock syndrome during a holiday in the US when she was about 17.
All her hair fell out and her fingernails, and when her hair grew back it grew back curly rather than straight. She was very lucky and suffered no other permanent damage/effects as far as I know.
I’ve heard of and known people whose hair went from straight to curly, or otherwise changed texture, after they lost it due to chemotherapy. I also know a woman who cut her straight hair very short (almost shaved) in college, and it came back in very curly. So it can happen, apparently for different reasons.
That conversation I overheard was the first, and until now, the only time I ever heard of this. I know that hair color can change as we get older, but I never realized that straight could become curly and curly could become straight.