I'm on some tortoise groups & the people on them just throw a fit if you mention that you want to put something on the shell because the shell is living tissue that breathes & putting something on them may clog up the shell. They say if they have the right diet & are hydrated they shouldn't get dry, yeah ok but how come mine had the right diet but got dry anyway?
The turtle or tortoise shell is keratonized tissue similar to our fingernails or a horse's hoof. Sometimes it gets dry!
My Shell E got very dry at one point, she's my first one that was broken by a dog, she had to live in the house in unnatural conditions, humidity inside the house in winter can get pretty low.. she had the right food, had water but still she got dry!
So I tried a hoof cream & it didn't work. Vitashell is kind of expensive for that tiny jar & the ingredients are not all that different from a hoof cream. I didn't try that because I didn't see the point if a hoof cream wouldn't work. So...
I smeared some essential fatty acid liquid which is made to be a supplement that you add to a dog's food, smeared it on her shell. After I rubbed it on & let it sit for about a minute I rubbed it off & then buffed her with a soft cloth. I did that 4-5 years ago & she's never looked dry again since. That may be something to think about & these essential fatty acids should be available in any store that sells dog food & supplies.
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PHRatz