Wikipedia “…the increase in ionic strength prevents some of the temporary skin wrinkling (partial maceration) which is caused by prolonged immersion of extremities in pure water. ….magnesium sulfate can also be absorbed into the skin, reducing inflammation.“
Magnesium sulfates are common minerals in geological environments. Some mineral waters have magnesium sulfates.
Studies on the benefits of Magnesium Sulfate are not common. I found one study from The Magensium Web Site that showed that Magnesium levels are impacted by bathing in Epsom Salts. While obviously a biased site, I found it to be interesting and well written.
Here you can also find a pdf of the Magnesium Symposium Program held in 2010: The Role of Magnesium and Novel Cation Channels in Inflammatory Aspects of Cardiovascular/Renal/Metabolic Disease: From Molecule to Patient
The average US bath takes 8 gallons of water, so the recommended usage of Epsom Salts per bath is 10 oz but less or more has an impact of Magnesium levels. To raise manesium levels, you might want to do this 2 or 3 times per week.