Transdermal Magnesium Therapy. Transdermal magnesium therapy is an extremely effective modality for health maintenance. A form of magnesium therapy which involves absorption of magnesium through the skin, transdermal magnesium is usually applied with magnesium chloride, a highly soluble and pure form of magnesium. Transdermal magnesium chloride therapy can be used effectively for a wide variety of health-related applications.