Just in case people are still reading this thread - not sure about sulphur etc that others mentioned, but mag oil absolutely works for me!!
I follow a keto diet and my body no longer had to hold on to so much water. Out with the water goes electrolytes (same with athlete's who sweat them out), so I use mag oil to keep me from getting cramps. It absolutely is absorbed through my skin. Also it is key to use every day, or often. Be prepared for a sting and slight burning sensation from the salt - goes away as your deficiency does. I make a mix of half and half mag oil and set n me free body wrap solution. Keeps skin tight. I put it on after I shower every day. This is more convenient for me than epsom baths.
Other benefits I can vouch for:
Gets rid of leg cramps
Far less bloat
Makes me skinnier (some believe it heals insulin issues, I believe that is the case here)
Calms my anxiety, others say cured their depression