I have 2 friends that are allergic to shellfish and that does include sea salt unfortunately.

Oh and yes you can be allergic to sea salt. I have spoken to several doctors about this issue. Even though there are copepods in drinking water, there are too few to create a reaction. We are essentially talking about salt harvested directly from the ocean, spread out to dry in the sun and sold. This definitely has plenty if copepods and other amounts of shelfish etc that causes a reaction.
Before discounting someones food allergy, do more research. Not everyone know everything in the world. The people who the allergies are happening to have a vested interest in researching the cause, so they are more likely to get to the bottom of it.
Check this out… harvesting seasalt directly from the ocean.
https://thecapecoop.com/foraging-harvesting-sea...

I am allergic to shellfish and fish. I cannot eat sea salt. I get very sick. Lots of pain in every joint. But I can have table salt, no problems. Too many products have sea salt now. I have to find no salt products or those made with regular salt.

I am also allergic to sea salt. I know all salt is essentially sea salt, but the salt harvested directly from the ocean and sold is to what I have an allergic reaction. I am allergic to all fish and all shellfish and even the smallest amount of seasalt puts me into an anaphylactic response. It’s frustrating because almost every product that is organic or “healthy” contains sea salt. There are no allergy warnings on items with sea salt, so you have to read carefully.

You're right Patricia. I have MCAS and have been allergic to sea salt since 2011. It's a pain in the ass and I cook exclusively from home because of it. People who think you can't be allergic to it have not done enough research. Not only does it contain fish and shellfish particles, it can also be contaminated by microplastics. There were times in a flare where I couldn't get too close to the beach. I'm fine with more processed/filtered salt like table salt.