Although 'miyatsuguchi,' small opening in the side of some traditional Japanese clothing (located where the sleeve meets the bodice, below the armpit) at sides also came from the kosode of common folks, its origin is not clear as to whether it is for convenience of putting it on and taking it off, or some say it is for heat release and others say it is an invention of prostitutes.
また、脇に「身八つ口」をつけるようになったのも庶民の小袖が発祥なのだが、この起源は着用の便宜を図るため、放熱のため、または遊女の発案によるなど諸説あり起源ははっきりしない。