You need to take a shower or bath every once in a while to stay clean. I love baths because not only do they get you clean but they are relaxing and comfortable too. Try to upgrade to that bathtub quickly. Also it's good to have two bathrooms in your home as soon as you can afford it, so someone can be using the toilet in one and taking a bath in the other one. Just like in real life :)

Note if you go too long without taking a shower, you begin to have green fog wafting up from you!!

The Sims 2 Tips, Techniques and Walkthroughs