**Note that you should check out some of these links as there is other information on how to actually bathe your rats if its really necessary and other information that is useful.

From: The Dapper Rat

Do rats need to be bathed regularly?

Rats don't actually need baths as they groom pretty much all day to keep themselves clean. But there are times you might need to bath them, like:
·If they get something yucky on their fur you'd rather they didn't groom off and ingest
·If they like to marinate in pee soaked bedding and end up stinky
·If it's for medical treatment, like a bath for a skin condition or to treat for parasites
·In preparation for a rat show
·If they are overcome by "buck grease" i.e. that orangey - oily male hormonal skin discharge
·If they are old or incapacitated and aren't grooming themselves sufficiently
·If it's really hot and you need to cool them down
·If they actually enjoy it... believe me, there are actually some rats who do love baths

From: http://ratguide.com/care/grooming/bathing.php

Bathing Your Rat
A Clean Rat is a Healthy Rat.
For the most part rats tend to clean themselves and often their cage mates. Some rats are not as fastidious about grooming as others and will need periodic maintenance. And on occasion, even the cleanest of rats may need some assistance with their personal hygiene.
The first thing to pay attention to concerning the cleanliness of your rat is its environment. Even a rat that religiously self grooms will become dirty if the bedding or flooring of its environment is not kept clean.
Sometimes a full bath is necessary. At other times a "sponge bath" or a tail cleaning is more appropriate and often less unsettling to the rat.
Please take care not to over bathe your rat as this will deplete the natural oils and cause the skin to dry.
Keeping the bath time short and soothing your rat will help to minimize stress.

Specific reasons to Bathe
1. Overweight, injured, ill, or elderly rats: These rats may be unable to self groom. Be particularly attentive to grooming when these issues are the reason for lack of grooming. Poor hygiene may complicate existing health problems or lead to additional health issues. Particular care needs to be taken when cleaning older rats or those with health issues.
2.Dominance urination: This behavior leads to the need for bathing especially in male rats.
3.Medical reasons: Such as: preparation for mite treatment, application of medical shampoo, parasitic relief, or treatment of other skin problems.
4.Orange back: Some intact males can get an excessive build up of yellow/orange oils on their backs (a product of testosterone related sebaceous gland secretions) .
5.Showing: Bathing a few days prior to a show will insure a good clean coat. Do not bathe too close to show day as it will not give the rats natural skin oils a chance to get back on the fur which may give the coat an unattractive dull or wispy appearance.
6.Odor control: Sometimes rats just are not good self groomers or have a natural odor that is muskier than usual.
7.Introductions: Bathing may help lessen territory issues when introducing new rats.
8.General Messiness: Sometimes your rat just gets into things on its fur/body that just need to be washed off.

From: http://www.rmca.org/Articles/qna2_01.htm

Question: I was told I need to bathe my rats before a show, but not too soon before a show. When and how am I supposed to do this?

Answer: You don't have to bathe all of your rats prior to a show. Most females stay pretty clean and have nice, soft coats that don't need bathing at all. You may just have to clean a female's tail up before taking her to a show. How ever, that's not normally the case with intact males.
Males that still have their testicles produce a lot of testosterone, which can cause some males to have extremely oily coats. You will see this as a yellow-orange, almost waxy substance on the rat's back, from about the center of his back to his tail. Rats with this problem definitely need to be given a bath before showing them in either the pet or show classes. Judges always like to see a clean rat on the show table, but it is imperative that the rat in a standards class be clean or points will be marked off. This is not normally the case with rats entered in the pet classes (individual clubs may vary on this rule), but still, judges don't want to see an incredibly dirty animal on the table at any time.
If you are going to show your pet, be sure to give him a bath about one week prior to the show. This allows some time for some of the oils to come back and make his coat soft and shiny. If you bathe him too close to the show, his coat will be dry and fly-away, and will not look nearly as nice. You're likely to get marked down for that in some clubs.

From: http://www.ratclub.org/ratcare_grooming.htm

Bathing Rats
For the most part, rats don't need to be bathed. They groom and wash themselves all the time and manage to keep themselves clean. Very occasionally there might be a reason to bathe your rat. Sometimes rats get up to no good and might get something horrible and sticky on their fur that you don't want them to ingest. Older and incapacitated rats might need help in that department as well. Always take into account the health and age of your rat. If your rat is unwell or frail, a full on bath might be too stressful for him. Try cleaning him with a damp cloth or baby wipes instead.

And the reason healthy normal rats don't need to be bathed:

From: http://www.ratbehavior.org/Glossary.htm#CCG
Cephalocaudal groom ("CCG"): Grooming sequence of face and body (common to all rodents). The rat starts by licking the paws, then rubs them over the head. This is followed by licking and rubbing the side of the body, the anogenital region, and the tail. The sequence may be anywhere from loosely organized to very stylized, performed in a similar or identical fashion each time. In rats, most sequences appear to be loosely organized. The grooming sequence may be interrupted at any point, and it seems that rats usually stop before grooming their tails.

Article on Cephalocaudal Grooming and how baby rats learn it - too long an article to copy.

From: http://www.ingentaconnect.com/conten...cblk.alexandra

From the book "The Behavior of the Laboratory Rat" (sigh, its in PDF so I have to retype - ouch!)

Natural grooming in rodents is an advantageous behavioral model useful for studying the organization and neural mechanisms of movement sequences. Grooming consists of complex strings of movements to clean and maintain the fur and skin of the body; these movements include wiping, licking and scratching. Grooming is natural and ubiquitous. It is observed readily; rats spend up to half their time during waking hours engaged in grooming (Bolles, 1960). Most grooming bouts are initiated by paw-licking or face-washing movements that proceed to grooming of the fur around the hear, neck and body in the cephalocaudal step-wise pattern (Richmond and Sachs, 197. Unitary grooming actions such as scratching or direct contact with the trunk are emitted on their own in some instances; however the cephalocaudal succession of grooming actions across the body surface is most frequent and well established.