The [Rama says](https://he.wikisource.org/wiki/%D7%A9%D7%95%D7%9C%D7%97%D7%9F_%D7%A2%D7%A8%D7%95%D7%9A_%D7%90%D7%95%D7%A8%D7%97_%D7%97%D7%99%D7%99%D7%9D_%D7%9C%D7%97_%D7%92) (OC 38:3) that one must protest a woman's putting on Tefillin. The Magen Avraham there (sk 3) says that this is...:

>מפני שצריכין גוף נקי ונשים אינם זריזות להזהר...  
>...because [Tefillin] require a clean body, and women aren't quick to be careful [about this].

What kind of cleanliness are we talking about? It's kind of hard to believe that women (even 400 years ago) would need to go to the bathroom uncontrollably.