Bamboo socks can shrink if they are not taken care of properly. As much as most people machine wash and dry their clothes nowadays, you can never go wrong with handwashing and sun drying your socks.
If you over-dry your socks, this can lead to shrinking your socks. If you want to tumble dry them, your safest option is to set it to mild or air tumble. When it comes to ironing, it is never necessary to iron bamboo socks.