Why don't sheep shrink when it rains?

If the things we make from wool shrink after getting wet, shouldn't the wool shrink while it's still on the sheep's back, too?

There are two main things that help the wool on a sheep's back to not be affected by water the same way as your wool sweaters: One factor is the way the tiny fibers grow on each strand of wool. As a sheep's hair grows out of its back, the fibers of each strand, which are scaly, point out towards the same direction. However, when wool gets woven together into a sweater, all of these strands and their fibers suddenly point into many different directions! When the wool gets wet and then dries, the fibers that point in opposite directions latch on to each other and lock closer together, meaning all the strands of wool pull together tighter than before, and your wool sweater shrinks up! The other factor that helps a sheep to keep his or her coat from shrinking is lanolin, an oily substance produced naturally by sheep. The lanolin keeps the scaly wool fibers slick and helps prevent them from locking together!

Thanks to these helpful things, a fluffy, wool-covered sheep can definitely get wet without having to worry that he or she might shrink up! -- PHEW!!

(by Mya Kagan, Whyzz writer)