Ringtail This is a condition in which portions of the tail become constricted causing the appearance of rings.  Ringtail is caused by an overly dry environment and can cause permanent damage if not treated. Advanced Ringtail Environmental changes should be made at the first sign of constriction to prevent the condition from progressing to this advanced state. Photo from DORA Recommended treatment: You should increase the humidity by using a humidifier, offer lots of juicy foods such as watermelon, and rub olive oil into the tail several times each day until the rings disappear.  If your rat has a history of ringtail, you should make permanent changes to their environment such as always running a humidifier or switching to a bedding that is less dry. To link to this page: http://www.raisinrats.com/medical/ringtail.html