On my Patreon feed, Joanne asked: Why do my Dead Sea bath salts get wet when I add essential or fragrance oils" But the store Dead Sea salts with essential or fragrance oils stays dry" 

Good question, and one that I had to learn the hard way! Dead Sea salts  (DSS) are hygroscopic or behave as a humectant, drawing water from the atmosphere to itself. That's great when you want extra hydration for your skin in the bath, but not so great when you forget to completely seal that 10 kg bag you have in your workshop.

The problem isn't about using fragrance or essential oils: It's all about the amount of DSS used and how they are stored. All the products I looked at in a Google search were quite well sealed with zip lock type tops or in jars with screw on lids. I couldn't see any ingredient lists other than "Maris sal", which means sea salt, so it could be all DSS or a combination or none, theoretically.
When it comes to using these salts, please keep them at less than 10% of your total salt amount and you should be okay. Seal your products well. (A cellophane bag with a twist tie or ribbon would not be considered "sealed well".)  As usual, your mileage may vary as it is dependent upon the amount of humidity in your environment. I live in a very humid place, so people in more arid parts of the world may have no problems at all with higher amounts.

*How did I learn the hard way" I made emulsified salt scrubs during the height of ...