Hygiene
After a while, Sims start to get dirty, and if they get very dirty, they start sniffing themselves and saying, "Ewww!". Bad hygiene will seriously affect Sims' mood and social skills—bad hygiene won't get a Sim promoted at work either. Therefore, it is necessary to take a bath or shower when the Hygiene meter slips into the red—a hot tub also works, but not as well, although it can boost the Social and Fun bars. Washing one's hands after going to the bathroom also improves this rating, as does brushing teeth[TS] or gussying up in the mirror.[TS2] In order to facilitate the latter activities, be sure to have a medicine cabinet, bathroom cabinet or mirror and sink. Sometimes, the shower leaks after a Sim has been in it, so it's handy to have a mop ready.
Hygiene on community lots
Most community lots will not have any ways of increasing hygiene other than sinks. In The Sims: Superstar, some Studio Town lots have steam baths and hot tubs, but none of them boost hygiene sufficiently. Therefore, it's best to get the Hygiene meter as full as possible before going out.
In The Sims 2, Sims with less than 2 Neatness points will take a sponge bath on community lots if their hygiene meter drops to the point where they begin to stink. This action is completely autonomous and cannot be prompted; Sims will proceed to the nearest sink to bathe themselves.
Bathing isn't a problem on Vacation Island, as most lots at least have showers, and resort lots have baths. Likewise, it's not a problem in the Bon Voyage vacation destinations, because there are baths and showers in the hotels.
Hygiene and other Life states
Servos,[TS2:OFB] PlantSims,[TS2:S] and SimBots[TS3:A] have no Hygiene motive. Bigfoot[TS2:BV] is largely indifferent to his own Hygiene, and will not bathe unless directed to by the player.
Other ways of affecting Hygiene
In The Sims, The Sims 2, and The Sims 3, there are alternative ways of raising, or maintaining, Hygiene.
In The Sims: Makin' Magic, magical children can use the No More Puddles? charm to take a magical "bubble bath". For adults, the Magic Mood charm can boost all motives, including Hygiene. In The Sims 2: Apartment Life, the neutral spell Cleanus Corpus boosts a Sim's Hygiene.
In The Sims: Livin' Large, the blue potion that can be made with the chemistry set maxes out three random motives, though there is no way to be certain that Hygiene will be one of them. In The Sims 2, Sims can use The Eclectic and Enigmatic Energizer to raise all motives, including Hygiene. In The Sims 3: Ambitions, Sim inventors can also invent the Floor Hygienator, which is placed on the floor and improves Hygiene levels slightly when walked over.
In The Sims 3, a Sim can buy the Dirt Defiant Lifetime reward (for 15,000 Lifetime Happiness points), which will make it take longer before the Sim with that reward has to take another bath.