Pale blotch on the shell

[Symphony]

Hello!

My pom, Walnut, has a weird white-blueish blotch on their shell.
I only noticed it today, which is weird considering it's size.
The affected part of the shell has the same texture as the rest of it.
The blotch disappears if I wet it but comes back soon after, like a hard boiled egg.

Here is what it looks like:
imgur.com/a/2jfzPvA

Does anyone have an idea what might be the cause? What should I do?

[Rasplutin]

I do not think it is anything serious or harmful to your snail.
If you make the shell wet and use a piece of tissue paper, can you wipe off the blueish layer?
I think it is something that was dissolved in water and remained on the shell when the water evaporated.
But I have no idea WHAT it might be... Looks like your Helix has taken a bath in not-so-clean water.

You probably did not notice the layer before because your snail's shell has always been wet when you looked.