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The importance of magnesium and the positive effects of magnesium substitution in various diseases are extensively documented (1,2). Magnesium compounds are widely used as medicinal and dietary supplements. The effectiveness of oral magnesium substitution for the treatment of magnesium deficiency is beyond controversy. However, the scientific seriousness of oral magnesium substitution has become questioned for several years through intensive marketing of magnesium-containing sprays for topical application. In both, specialist and lay press and on the internet, there are increasing numbers of articles claiming the effectiveness and superiority of magnesium oil over an oral magnesium intake. Magnesium oil is not a real oil but a concentrated magnesium chloride solution which is sprayed on the skin. The transdermal absorption of magnesium in comparison to oral supplementation is presented as being more effective on the one hand due to nearly 100% absorption and on the other hand as it is associated with fewer side effects because of bypassing the intestinal tract. For proving this, various publications are mentioned.
Magnesium absorption by skin
The skin forms a biophysical barrier towards the environment and is therefore responsible for the separation between "inner" and "outer". This means that the absorptive capacity of healthy skin for substances from the outside is very limited. This is evident particularly in the limited application for topical drugs. To get through the skin, a substance must penetrate the epidermis or has to be absorbed by sweat glands or hair follicles. The outer layer of the epidermis is the stratum corneum. It consists of dead cells which form together with the paracellular deposited fats a waterrepellent protective layer. Overcoming this layer in significant quantities is only possible for lipophilic substances. In a magnesium chloride solution, magnesium is present in ionized form and therefore not able to penetrate a lipophilic layer. In addition, magnesium ions have a large hydration shell so that an unregulated passage through cell membranes is nearly impossible. Therefore, cellular magnesium uptake is only being carried out by specific magnesium transporters and not by diffusion. However, since dead cells of the upper skin layer do not contain functional magnesium transporters, magnesium resorption may be possible just at the small area of sweat glands and hair follicles. A recently published study from Chandrasekaran et al. showed...