Tumors are common in rats, but so are abscesses and cysts.  If you suspect a lump on your rat’s body is a tumor, it’s worth it to wait 2-4 weeks to see if it is an abscess or cyst instead.  Most abscesses are fairly harmless and either clear up on their own or with minor treatment.  Generally cysts are also harmless.  Abscesses can “pop up” overnight and they tend to grow more quickly than cysts or tumors.  With most tumors on the body the skin moves slightly independently of the lump, but abscesses or cysts are usually inside the skin so moving the skin moves the lump.

 

Abscesses are usually small infections, often caused by bite or scratch wounds, which the skin encapsulates to isolate.  The wound usually heals before the abscess appears.  However, sterile abscesses can be caused by inflammation due to an injury or a foreign body, such as sutures.  After a rat has been neutered, a sterile abscess in the scrotum is common and can be treated as a simple abscess.

 

It is fairly common for male rats to develop abscesses in the groin area.  These often are noticed only after the abscess opens and drains and therefore appear as a hole in the skin.  In most cases, groin abscesses heal quickly once they open and drain.

 

An abscess on the face, in a tooth socket, or near lymph glands, can be more serious, often indicating a cancer.  Oral antibiotics should be given for a serious abscess.

 

An abscess that won’t heal after a week or two of treatment may be a cyst, a sterile abscess caused by a foreign body, or it may indicate a cancer, such as squamous cell carcinoma, especially on the face. You can try to treat a cancer with prednisone at 1 mg/lb twice a day, which in some cases can shrink or slow the growth of a tumor, and try to control the infection with antibiotics, but there is no cure.

 

A Simple Abscess

 

In rats, an abscess on the body (including the scrotum) can usually be allowed to progress on its own. The body has a natural healing process to open the abscess so it can drain. This process may take several weeks, but as long as the rat seems well and isn’t bothered by the abscess you don’t have to do anything. Abscesses on the underside of the body generally progress more quickly because gravity helps the opening process. Abscesses on the back can take much longer to open.

 

The first sign that the abscess is starting to open is often a dark area on the top of the lump.  Most commonly, the skin on the top of the lump will die and turn dark, hard and “crunchy.” Eventually the disc of dead skin will fall off leaving a hole, often quite a large hole, leading to a pocket. This is all okay.

 

In most cases, the pus will drain out and the rat will lick the pocket clean, so you don’t have to do anything.  The hole will usually heal up in a few days.  Sometimes, the dead skin will not come off completely and will need to be cut away.

 

This small abscess on my hairless rat’s ear (photo #1) took quite while to open.  I took the first photo on 9/25/10, and you can see the yellow pus through the thin layer of skin over the top of the lump. The next photo (photo #2) was 12/23/10. I finally got tired of waiting and squeezed it out. You can see the blob of pus that came out. The black dot on Munchkin’s shoulder (circled in blue) is a tiny sebaceous cyst.

 

Photo #3 is a sterile abscess that developed after a neuter due to a reaction to the sutures.  See the dark spot where the hole will form.

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Helping an Abscess

 

If you want to speed up the process of a developing abscess, here are some things you can do.  First, carefully trim the hair away from the lump; then apply a hot compress twice a day to help bring the infection to a head so it will open and drain. To make a hot compress, wet a cloth with water as hot as you can stand, or fill a latex glove with hot water. To reheat the compress, microwave it for a few seconds.  Always test the temperature on your forearm first; then hold it against the lump for as long as your rat will let you. You can also apply an acne treatment containing benzoyl peroxide, or Swedish bitters (an herbal mixture), to the top of the abscess daily to help it open.

 

Treating an Abscess

 

In some cases when the abscess is open, the pus will be too thick for the rat to clean out so you need to clean the abscess by gently wiping out all the pus with a cotton swab. This usually does not cause the rat pain. If it does, try applying some Bactine. For small abscesses, you can make your own tiny cotton swabs with cotton and a toothpick. Cut the sharp tip of the toothpick off and twirl a bit of cotton around it.

 

Next it’s a good idea to flush the wound with Betadine diluted with 5 parts water or hydrogen peroxide diluted with 10 parts water, using a syringe without a needle. Then put a tiny dab of antibiotic cream (such as Neosporin Plus) inside the pocket, spreading it evenly with a cotton swab. Remember that the rat will lick the wound, so don’t use too much cream.

 

Repeat the hot compress soak, cleaning, and antibiotic ointment twice daily if an abscess is open, but doesn’t heal right away.  An abscess must heal from the inside out.  If the skin heals over the opening too quickly, the infection will recur.

 

On rare occasions, an abscess will come back.  Should this happen, treat the rat with oral amoxicillin and/or enrofloxacin. If this doesn’t clear the abscess up, I recommend that your veterinarian do a culture and sensitivity test to determine the best antibiotic to use for the infection.

 

Tooth Abscesses

 

Any swelling or pus in the mouth near a tooth could indicate a tooth abscess and should be treated immediately by a veterinarian.  It is a tooth abscess if the tooth comes out easily when pulled.  While the tooth must be removed, it will still be difficult to cure the infection remaining in the tooth socket and jaw. Without immediate and aggressive treatment, the infection can be fatal. A powerful antibiotic good for anaerobic bacteria, such as metronidizole or clindamycin, is necessary. It is helpful to have your veterinarian do a culture and sensitivity test on the infection to find out what antibiotics are best.

 

Cysts

 

A cyst is a sac filled with a liquid or semi-solid substance. The most common type of cyst found in rats is the sebaceous cyst.  These cysts develop from sebaceous oil glands in the skin. They are most often found in male rats whose sebaceous oil glands are more active, and usually located on the back or side. These cysts look much like a small abscess, although they fill with waxy or oily sebaceous secretions, not pus.

 

Sebaceous cysts tend to grow more slowly than abscesses or tumors and usually don’t get as large. Most sebaceous cysts eventually develop a small hole in the top that can appear dark because of dirt on the secretions inside the cyst.

 

Sebaceous cysts typically don’t cause the rat any pain or problem, but if a cyst continues to grow, it should be emptied to keep it from getting too big. (I once saw a sebaceous cyst on the back of a female rat that the owner thought was a tumor because it was about 1½ inches long!)  A cyst will recur until its internal sac is destroyed. Keep squeezing the cyst and it will eventually go away.

 

 

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Left Top Row:

 

3 photos of tiny new sebaceous cysts.  Of course, they are much easier to see on hairless rats.

 

Left Bottom Row:

 

Here’s a little sebaceous cyst that I squeezed out, showing all the stuff that came out, and what it looked like afterwards.