Myth or Reality—Transdermal Magnesium?
— Read on www.ncbi.nlm.nih.gov/pmc/articles/PMC5579607/

Looks like Magnesium works best in the diet or as a vitamin supplement.

All the testing, in the above study showed topical applications to be a myth.

So maybe stay away from scams about magnesium absorption through the skin.

The above article is kinda dry, but very informative.