A turtle's shell is composed of about 60 bones. The bony shell is covered with a thin layer of epithelium, which produces the hard outer shell layer, called the scutes. The scutes are plate-like scales similar in composition to the keratin of fingernails. They protect the bones and epithelium of the shell underneath. As the turtle grows, the epithelium produces a new scute beneath the old ones that is a larger diameter than the one layered on top of it, allowing the shell to expand.
In most turtles and tortoises, the scutes remain on the shell for life, which causes the shell to thicken and protects it. The outer layers of scutes can be worn down, especially in burrowing tortoises, but are not normally shed. In many species of water turtles (Genera Chrysemys, Deirochelys, Graptemys, Pseudemys, Trachemys and Malaclemys), however, they shed the outer layer of scutes annually. This keeps the shell from getting so thick and heavy that it makes it hard to swim, and it also helps to rid the shell of coatings of algae and other things that grow in an aquatic environment.
It's perfectly normal for water turtles to shed their scutes as they grow. But a peeling shell can also indicate disease, depending on the type of turtle and whether it's healthy.
In addition to shedding scutes, all turtles and tortoises shed the skin on their legs and necks. A turtle's skin is different from yours because it's not elastic and doesn't stretch to allow for growth. As turtles grow, you'll see that they outgrow and shed their old skin in stages. This is most noticeable in aquatic turtles, and it also serves as a way to stave off infections
Why Do Turtles Shed Their Scutes?
Healthy shedding occurs as part of a water turtle's normal growth, as the shell expands with the rest of its growing body. Other common reasons for shell problems include bacteria, parasites, algae, environmental issues, and poor nutrition. It's important to be able to distinguish healthy shedding from problems that could endanger your pet's health or life.
First, determine whether the shell under the peeling scutes looks normal. Anytime the shell looks deformed, reddened or bloody under the scute, has exposed bone, or the shell feels soft or spongy, there's a problem and you should seek veterinary advice as soon as possible. You should also see a vet if your turtle is continuously shedding scutes or the scutes are peeling but not falling completely off.
Peeling as part of the growth process is normal as long as the thin layers come off, revealing shell that looks and feels normal.
- Scutes should generally be intact and whole and not come off in parts. If they don't, it could be a sign of disease. Be aware that sharp rocks can damage your turtle's scutes or cause it to prematurely shed, so ensure that nothing in its environment is potentially dangerous.
- Shed scutes should not be very thick and should appear almost translucent. Essentially, they should look like the shell where they come from.
- It's normal for a water turtle to eat some of its scutes after they fall off. But to be safe, remove shed scutes from the tank as they could damage your turtle's throat and internal organs.
Health Issues That Cause Shedding
Dysecdysis (abnormal shedding) can leave your pet's shell exposed and vulnerable to infection. It can also be a sign of liver, kidney, thyroid, or bone disease, or a nutritional deficiency. Bacterial shell rot is another serious problem, which can lead to permanent shell deformity. Other reasons why your turtle might shed abnormally include:
- Overfeeding, which can lead to too-rapid growth or other health issues
- Injuries caused by sharp rocks or the like in a turtle's environment
- Basking in an area where it's too hot
- Too low of environmental temperature
- Fungal and bacterial infections
- High ammonia levels in the turtle's water (It's important to have a good filter with biological filtration)
Treatment depends on the severity and cause of your turtle's dysecdysis. If the problem is relatively mild, start by ensuring that conditions in your pet's habitat are optimal. In some cases, minor changes to your pet's enclosure can eliminate the problem. Check to be sure that:
- There are no sharp rocks or other items that can cause injury
- The ideal temperature is maintained and there are no "hot spots" that can injure your turtle
- Your water filter is of good quality, works properly, and filters biological as well as chemical contaminants
- You are feeding the correct diet
If the problem is more serious or is not alleviated by changes to the habitat, it's best to check with the vet. While it's possible for you to remove fungi and algae from your turtle's shell, it's easy to injure the shell. It's best to have an expert handle the problem. Your vet may also be able to diagnose an underlying medical issue and prescribe medication.
One of the more common treatments for shell rot is debriding: a process of gently cleaning off the rotten shell and then treating the underlying tissue with antibiotics such as silver sulfadiazine cream. Vets may also give the turtle an injection of ceftazidime or another antibiotic. Some turtles need regular debriding (along with a proper habitat and nutrition) while the shell heals. If the turtle's shell is fractured or has deep rot, vets are often able to patch the shell until it grows back on its own. It may take months for a shell injury to return to normal.
If you are cleaning the shell yourself, use a very soft scrubber such as a soft toothbrush and work very slowly and carefully. If you don't have access to antibiotic cream, another option is an antibacterial ointment such as Betadine or Povidone-Iodine. Once debrided, a turtle should be kept dry and warm for a few days, but with access to a small bowl of water for drinking. This process may have to be repeated several times over the course of a few weeks. If, after several debridings and use of antibacterial ointment, your turtle is still showing signs of shell disease, visit your vet.
In many cases, there's no need to prevent scute shedding. It's a necessary and important part of water turtle growth and health. To avoid problems, however, it's important to maintain an appropriate environment for your turtle and check in with a vet as soon as health issues arise.
Disorders and Diseases of Reptiles. Merck Veterinary Manual.
Shedding Management for Companion Reptiles. Companion Animals, Cooperative Extension, U.S. Food and Drug Administration.
Palmeiro BS, Roberts H. Clinical approach to dermatologic disease in exotic animals. Vet Clin North Am Exot Anim Pract. 2013 Sep;16 (3):523-77. doi:10.1016/j.cvex.2013.05.003