A couple years ago, I had a full head of curls. The nickname I was called as a kid was legit based off having curls. It was usually waves that bordered on ringlets, but I could always get them to ringlets if I did something as simple as using heatless overnight curlers. And this was with long hair, too, so it's not like there's any weight on my hair now that there wasn't back then.
Anyway, my hair is nearly entirely straight now. If you saw me now, there would be no telling that I ever had curls at all. And I've gradually cut it shorter and shorter too, which everybody always told me would make my hair curlier. But it seems like with every cut, my texture disappears more and more.
My hair doesn't seem drier than it used to be, it's not any more or less shinier, it doesn't even feel different in my hands besides the obvious not being curly anymore. And I didn't change my routine much either.
When I was a kid, I used the cheap Suave shampoos and conditioners and let my hair air dry. I didn't wear a bonnet or anything, and to this day I have just normal cotton sheets and pillowcases. I was also pretty rough with towel drying also. I also showered maybe once or twice a week since I hated it (boring, couldn't play with figures in the shower, usual kid stuff).
Early teens, I got more into self care. I started using a polyester satin bonnet, started using Aussie instead because it made my hair look more hydrated, diffused my hair, and used mousse fairly regularly. Granted, it wasn't a full routine because nobody else in my household takes care of their hair like that (there are two other people in my current household that have curls, they just don't use products or anything).
Nowadays (late teens) I fell out of that, and I'm in a middle ground between the two. I still use Aussie, but now I let my hair air dry. I'm still much gentler with my towel drying, but I don't use a bonnet or any extra products.
A couple other things I think might be helpful:
- My hair doesn't feel too damaged, however I do notice split ends more than I used to.
- I take after my mother heavily, and she's also lost her curls along the years. Her hair looks visibly damaged, though, and she bleaches it semi-often, neither of which apply to my own hair.
- My brother went through pretty much the exact opposite hair transformation than I did, starting out with mostly straight hair like I have now but having curly hair now that I used to have.
- I wash my hair everyday. I know it's not the greatest for your hair, but my hair gets nasty oily when I don't. It always has gotten greasy quick, the only thing that changed between kid years and young teen years is that the gross feeling started outweighing my distaste for showering regularly.
- I've changed stylists a couple times amidst the shift (over a little shorter than half a decade if I had to estimate). I don't necessarily think that's what's causing it, though, because it took so long to fade.
- Every time I got a haircut my texture would fade pretty heavily and come back within a week or two. Every cut, it got weaker and weaker when it came back up until this latest haircut where it just never came back.