American Fancy Rat & Mouse Association

This article is from the Spring 1997 AFRMA Rat & Mouse Tales news-magazine.

Scabs . . . Diet or ?????

By Nichole Royer

It all started with an innocent trip to a pet store (doesn’t it always). I didn’t even go to look at the rats. Whenever I am in Berkeley, I try to make it to the Bay Area Vivarium, one of the largest reptile pet shops in the world, to have a look at their huge collection of reptiles. (It’s better than going to the zoo, and they don’t even charge admission.)

On this particular trip I happened to notice there was a lab cage full of 10-week-old Blue rats sitting on the front counter. This was some time ago (February 1994), and it was still unusual to see Blue rats in pet stores, so naturally I had to go over and have a look. When I got close, they all ran over and poked their noses out, so I gave them each a head scratch. I quickly noticed the only one in the cage with a white spot on his head, who insisted on showering me with kisses.

Repeating to myself that I was not going to take a rat home, I wandered through and looked at all the herps. As I was preparing to leave, however, I had another run-in with my little blue and white friend, and this time he was being lowered into a tank with a python. Needless to say, after giving the pet shop worker a lecture on the evils of feeding live rodents (with the full agreement of the pet shop owner), the Blue rat drove back to L.A. with me!

Thus was my introduction to Willie. His addition into my colony went without a snag, and he proved to be a gentle and loving companion for my elderly Sebastion. Considering his background, I was very surprised that he was extremely healthy and loving.

The Start of the Problems

The problems started when Willie hit the 6-month mark. I didn’t even notice him scratching much, but all of a sudden there they were—scabs—and lots of them. They appeared overnight on his chin and shoulders, with a few on his back. I shouldn’t have been surprised as this is a very common problem, which males (particularly Blues) are prone to. Since there were no signs of any parasites on Willie or his roommates, I followed the advice I have frequently given to others with this problem. First, clip the rats’ claws and give them a bath (I use a diluted solution of kitten flea shampoo to be sure the problem is not caused by parasites). Then, put them on a strict diet of lab blocks and only healthy treats. No peanuts, sunflower seeds, dog food, grain, or any other high-fat, high-protein foods. As usual, this worked well, and the scabs virtually disappeared. Naturally, if this had not been successful, Willie would have been off to see the vet.

Why Does This Happen?

Scabs have been a problem in the fancy from its beginning (in England they often are referred to as spots). For years fanciers have maintained that it is diet related, as all the evidence has pointed to that answer. In the past, anti-parasitic products have had very little effect on these animals, but limiting the diet has worked wonderfully. There have even been a number of cases where people have spent small fortunes at their vet to try to find and cure some form of parasite, only to have the scabs disappear when the diet is changed.

I have always been curious about the cause of this condition. Many breeders have discovered that certain colors are far more prone to it than others. There is also good evidence that it is genetic and runs in families. Breeders who have worked with animals who develop this problem, report that it can be eliminated by only breeding those animals who do not develop scabs. I always wondered if it could be an allergy to something in high-protein, high-fat foods (I have also had the problem flare up when I have given extra corn as a treat).

Major Breakout!

Willie was almost scab-free until he turned 2, at which time he developed a major scab problem. Not only were there scabs, but he started losing fur and making himself raw with scratching. I kept his claws trimmed, bathed him, and strictly watched his diet, but nothing worked. I was just about ready to take him to a vet, when I came across something in a pet shop that I thought might work. It was meant for hot spots in dogs and contained both hydrocortisone to stop itching, and tetracycline to prevent infection. I figured it couldn’t hurt to try it. I went home and sprayed it on the scabby areas of Willie’s coat and repeated the treatment 3 days later. In a week there were no more scabs! I was thrilled. I quickly discovered that by treating him once every 3 weeks I could keep Willie scab-free.


A while back I acquired some Ivomec. Since none of my animals had ever been treated for parasites (some have come from questionable sources), and the Ivomec was unlikely to harm them, I treated them all. (This is not a recommended practice, treatment of your animals should be done under the supervision of a knowledgeable vet.) As expected, the treatment had no detrimental effects; however, it did have a surprising outcome. My two rats with chronic scabs, Willie and Kiley, both stopped developing scabs. In fact, the scabs totally went away and have not come back no matter what I feed them! At almost 3, Willie is totally free of scabs and as healthy and happy as ever.

I have no explanation for why this happened. Neither rat had any sign of external parasites. Both rats had long term roommates who never showed any sign of scabs, and all have always been very healthy. Both rats had definite “flare ups” of scabs that were related to diet, and I could reliably predict when and how bad a flare up would be if I gave them a special treat out of the “no no” category.


Is it possible that some rats become more sensitive to some sort of mite or lice bite when they are fed high protein/fat foods? If some sort of parasite is involved, why haven’t any of my other rats shown signs of it? Why do other treatments for parasites like powdering, dipping, spraying, and bathing with flea products not have any affect on this condition, but Ivomec does? Why does this condition appear to be passed from father to son, and why does it usually only affect males? Why does it usually first appear when the rat reaches maturity (6 months) and then flare up again at 2 years? I would like to find the answers to these questions, and am very interested to hear from anyone else who has had similar results when treating with Ivomec, and particularly from anyone who Ivomec has not helped.

Do rats have the same type allergies to corn as dogs in causing scabs. What are the best ways to treat, other than taking away the corn in the diet and giving cortisone, etc.?

Answer: Comments on Scabs, Diet or ??? by Carmen Jane Booth, D.V.M.
I am unaware of any reports of rats having allergies from corn. Dogs and humans are very different from rodents regarding allergies. Most often, problems that rodents experience are from the bedding material or external parasites, rather than the diet. If sufficient time has passed after all environmental factors (caging, bedding material, external parasites, etc.) have been removed or changed, I would first suggest a short course of antibiotics to rule out a bacterial etiology (cause). Following this, if the rat still had problems, and the owner wanted to pursue an allergic etiology, then I would recommend feeding one of the hypo-allergenic dry dog food diets for 6 weeks. If improvement was noted, then I would slowly add in additional fruits, vegetables, and starches. I am a proponent of feeding rodents a mixed diet, based on either a high-quality rodent block or dog food (if no block is available), in combination with washed fruits, vegetables, and starches.

Using a combination of antibiotics and anti-inflammatory steroids, such as the tetracycline and hydrocortisone spray that Nichole used for refractory (difficult) skin problems, can be extremely useful. I would imagine that the spray is intended for dogs with “Hot Spots” from chewing themselves because of fleas. Anti- inflammatory steroids are extremely potent and powerful medications, and they are used extensively in veterinary medicine for puritis (itching) related to allergies or hypersensitivities. They are absorbed systematically through the skin and there are risks associated with them. In general, if an animal is otherwise healthy, a few applications will probably not cause any problems. The exact mechanisms whereby steroids act are unknown, but it is clear that they suppress, but do not abolish most, and possibly all, aspects of acute and chronic inflammatory processes. The side effects that may occur during treatment are related to the physiological effects. Some of the side effects include: increased water consumption (polydipsia), increased urination (polyuria), muscle wasting from protein catabolism, delayed wound healing, osteoporosis (decreased bone mass), bone fractures, increased appetite, and the decreased ability to fight off disease. Animals that are on chronic (long term) steroids, are particularly vulnerable to stress if treatment is terminated abruptly. Anti-inflammatory steroid treatment is palliative (provides relief), but not curative. Steroids are extremely useful, but should be used with care and preferably under the direction of a veterinarian. *

Go to Update: Scabs...Diet or ??? in the Winter 1998 issue.

Back to top

Updated June 15, 2021