Answer:
   
   While traditional Judaism has a number of practices that are hygenic,
   there appears to be only one that is motivated by hygene. There is a
   law called "machayim achronim" (water after [the meal]), a rule that
   one must wash one's hands after eating. The claimed reason for this
   law is that people tended to eat sodom salt with their food. [Our
   common table salt, sodium chloride, was quite expensive. The Roman
   army paid their soldiers in it! Thus the expression "worth his salt".]
   Sodom salt, whatever it is, could injure the eye, so one should wash
   one's hands after the meal to avoid blindness. Today, since we don't
   use this kind of salt anymore, most do not feel the law is in
   practice. Others still keep the rule, as there is an allusion to it in
   the Torah.
   
   However, other practices have hygenic effects:
     * There are seven distinct prohibitions involved in eating
       insects--they are less kosher than pork! People inspect their
       vegetables very carefully to get rid of all of them. Some Jews
       don't even eat brocolli or cauliflower because they are nearly
       impossible to inspect.
     * Right after you wake up, before doing anything else, you are
       supposed to wash your hands because: (a) your hands could be
       anywhere when you're asleep; and (b) sleep is a modicum of death,
       and there is a state called "tum'ah" (untanslatable) which is
       associated with death.
     * You must wash your hands before eating bread, so most meals are
       preceded with washing your hands. This is to get people used to
       being un-tamei (different conjugation of tum'ah, still
       untranslatable) when eating, which was necessary for eating from
       sacrifices, or if a priest or levite wanted to eat from their
       respective tithes. This washing is called "mayim rishonim", water
       before [the meal], and was considered less stringent than the
       post-meal washing (back when the latter was for health reasons).
       In general, Jewish law sees health as a higher priority than
       itself. (Barring three do-or-die commandments.)
       The three hand washing laws, upon waking up and before and after
       meals, had significant impact on survival during the Black Plague.
       Jews faired much better than the rest of the population. To the
       extent that it was taken as "evidence" that the plague was some
       kind of Jewish conspiracy, leading some to set arson and murder.
     * There are no sexual relations from the time menstruation begins
       until a week after bleeding stops. Before resuming marital
       relations, the wife immerses herself in a mikvah, a ritual bath.
       Before going to the mikvah, she must be entirely clean, so that at
       least in potential, nothing comes between her and the water. In
       practice, this means soaking in a regular bathtub for roughly half
       an hour, flossing, making sure her hair has no knots, and other
       things.
     * In many communities, men go to the mikvah the day before a
       holiday, and often on every Friday. (Most only twice a year:
       before Rosh haShanah, and before Yom Kippur.) Some immerse
       themselves before prayers the morning after having sexual
       relations. The preparations are less grueling, as these are only
       custom, while the post-menstual immersion has a biblical source.
       However, it still means that men in these communities bathed quite
       often, as these things went before indoor plumbing.