I'm allergic to crabs, shrimp etc but not to fish (salmon, tuna etc). is it okay to take kelp supplements for my thyroid?

Save your $$: Hi. Kelp supplements will do NOTHING for your thyroid that good old (cheap) iodized salt won't do. Save your money, and don't make the snake oil salesmen rich!

Doesn't matter: In the US, there is lots of iodine in the diet. Taking more iodine, in the form of kelp or anything else, will not help your thyroid. I suspect you will not get an allergic reaction, but why risk it? If your thyroid is underactive (based on blood tests--symptoms alone are unreliable) you need to take levothyroxine.