Have you ever wondered why wool shrinks?

Wool fibers have an outer layer of “scales” that shrink or “felt” when heat, moisture and mechanical action (agitation) cause the scales to interlock. When this happens it is nearly impossible to unlock them. That's why washing wool in a washing machine, even on delicate, often causes wool to shrink.

Hand-washing wool clothing
I prefer to hand wash wool whenever possible. I think things get cleaner and fresher this way.
This is how I wash a wool shirt.

1. Fill a sink with cold water. Add Woolite detergent as directed on the label.
2. Look for any extra-dirty areas. Dampen those areas and lightly rub with your fingers to pre-treat.
3. Submerge the shirt and gently agitate with your hands. It is important to use gentle agitation to avoid shrinkage. After a minute or so, let the shirt soak for a few minutes, then lightly agitate again for about a minute.
4. Drain the water from the sink and push down on the shirt to push out the soapy water. Don’t squeeze or twist out the water.
5. Rinse the shirt by lightly moving it around in cold water.
6. After the shirt is rinsed, push down on the shirt to remove water. Don’t squeeze or twist out the water.
7. Optional step: Place the shirt in your washing machine and use the spin cycle to spin out the remaining water. This works great with my washer because the shirt lays still in the bin and does not move around. If your washer doesn’t work like this, this is not a good option for you.
8. Reshape the shirt so the collar, pocket tabs, tails etc. are flat. Reshaping it while damp will help prevent the need to iron.
9. Lay the shirt flat on a drying rack, towel or hang to dry. 
10. After it has dried, the shirt is soft, springy and supple, it smells fresh and looks wonderful!