People have been using minerals like magnesium transdermally for thousands of years. Even though humans have been using the skin as a direct pathway into the body for treatment for centuries, but only recently have we begun to understand the science behind it.
The skin is the largest organ of the body, covering about 12-20 square feet and comprising approximately 10% of the total body mass of an average person. The primary function of the skin is to provide a barrier between the body and the external environment. This barrier protects against the permeation of ultraviolet (UV) radiation, chemicals, allergens and microorganisms, in addition to the loss of moisture and body nutrients. Think of it as both a giant barrier, but also a giant sponge under the right conditions.
Pores & Hair Follicles
The first way to get through the skin, a substance must penetrate the epidermis or has to be absorbed by sweat glands or hair follicles. The stratum corneum is the outermost layer of the epidermis consisting of dead cells (corneocytes). This layer is composed of about 15 to 20 layers of flattened cells. There’s a lot for vitamins and minerals to get through.
But, each square inch of our skin has 40-70 hair follicles and 200-250 sweat ducts. Plus, at any moment the skin is circulating around a third of all the blood in our body which means that when absorbed through the skin, we can absorb 40% more than if we took a supplement.
The other more common pathway through the skin is via the intercellular route. Nutrients crossing the skin by this route must pass through the small spaces between the cells of the skin, making the route more difficult that going through a follicle or pore. Although the thickness of the stratum corneum is only about 20 µm, the actual diffusional path of most molecules crossing the skin is closer to 400 µm. The 20-fold increase in the actual path of permeating molecules greatly reduces the rate of nutrient penetration.
By this route, nutrients cross the skin by directly passing through both the phospholipids membranes and the cytoplasm of the dead keratinocytes that constitute the stratum corneum.
Although this is the path of shortest distance, substances encounter significant resistance to permeation. This resistance is caused because the nutrients must cross the lipophilic membrane of each cell, then the hydrophilic cellular contents containing keratin, and then the phospholipid bilayer of the cell one more time. This series of steps is repeated numerous times to get through the full thickness of the stratum corneum.
If molecules are small enough, they can slip through the skin. A molecule smaller than 500 Daltons, can drift through the stratum corneum, the outer layer of the skin – the 500 Dalton rule. For example, Magnesium ions are significantly smaller than 500 Daltons, at an atomic mass of just 24 Daltons.
And molecules can be helped along even further when they are combined with a bath - water and heat. Water helps break down and reduce the molecule size of vitamins and minerals to help them more easily pass through the skin. Plus, our skin naturally pulls water into itself, so a bath leverages that love of water to pull nutrients in. Heat from the water also helps this process as well. First, warmth helps relax the strength of the skin membrane so nutrients can pass through more easily, and opens up our pores to help move vitamins and minerals through those natural pathways.