Male 58yrs. blood test 12 months ago showed underactive thyroid. been taking kelp (675mcg per day) have developed a facial/neck rash. kelp induced?

Kelp doesn't help: Hi. Kelp doesn't help any form of hypothyroidism except iodine deficiency; iodine deficiency is non-existent in the modern world. So you're doing nothing to help your hypothyroidism by taking kelp. Assuming the diagnosis of hypothyroidism is correct, stop the kelp and thane the thyroid hormone your doctor would have prescribed based on the labs showing hypothyroidism. Good luck!