Anecdotal stories that hormones can do this (via birth control in this example):
[link to womenshealth.about.com]

Xanax changing DNA:
[link to thisisyourbrainonpsychdrugs.blogspot.com]

Depakote changes DNA, too. I think this is related to people's hair changing from straight to curly and vice versa. Don't have a link on that at the moment.

Maybe your DNA has changed?

I'm sure if it's from drugs in the water or some other toxin, that there could be a way to combat it or at least fight further changes via nutrition.

I know that with some drugs you can take supplements to counteract side effects, so if you can pinpoint the nutrients related to hair texture maybe that could help you find a way to lessen the changes.