I have a cat. There is a possibility of cat hair getting mixed in. Thank you for your understanding. I believe this is a size M, but it's a hanjuban (half undergarment). It's a casual type of undergarment that can be worn in place of a nagajuban (full undergarment) with a han-eri (detachable collar) attached. The hem on both sides has been cut to allow the collar to be tucked in deeply. The cut edges are raw and look unsightly. Also, there is tape residue on the collar from where the han-eri was attached with double-sided tape. For those who can accept this.