I have in the past had occasion to have clothes shrink on me. In particular I have a pair of jeans around here that would fit a fourteen-year-old Callista Flockhart. How can I prevent this phenomenon, and is there any way to reverse it?
Wash you jeans in cold water, and dry them on low heat. If your jeans are really dirty, pre-soak them, either in the washing machine (if your machine has that feature), or in a bucket of water with detergent added.
Unlike knit clothing, there isn’t much you can do to reverse the shrinkage in a pair of jeans.
One can reverse the shrinkage of knits?
Depending on the kind of fiber and the amount of shrinkage, you might be able to stretch out the garment while it’s still wet. In my experience it’s easiest with cotton knits like t-shirts, but you can also do it with wool in many cases. Forget it if you have any shrunken synthetics like rayon, though - these garments are really unforgiving of a too-hot dryer.