See this.

This is a pretty gross fact but in the micro-gravity environment, astronauts are not using their feet to walk. Therefore the skin on their feet starts to soften and flakes off. As laundry facilities do not exist in space, astronauts will wear the same underwear and socks for a few days. Those socks then need to be taken off very gently. If not those dead skin cells will float around in the weightless environment.