Why do my jeans shrink when air-dryed? I never put jeans or pants within the dryer because they...

I never put jeans or pants within the dryer because they tend to shrink. In the past, I've never have a problem with jeans shrinking when I put them out to air-dry. However, I've be studying abroad contained by a foreign country this semester and everytime I let my jeans air-dry, they shrink, and deeply. The person I'm studying here next to also always air-dries, but she's not have the same problem, even though tons of her jeans are the same brand as mine.

What could be cause this? Difference in humidity? Material? How I'm wash them?
Answers:    It is probably difference in humidity. Is the other person's jeans like size or different as yours?