Transdermal Absorption

Applying magnesium to the skin is a comparatively recent route of intake. The exact path magnesium takes through the skin is not settled in every detail — but several studies have now addressed the question.

The three transdermal transport routes

Three routes are known for substances passing through the skin:

  • Volume diffusion — between the cells (intercellular diffusion)
  • Transcellular diffusion — through the cells themselves
  • Shunt diffusion — via the skin appendages, that is through sweat glands and hair follicles

Magnesium ions can in principle pass through the cells. According to the work of Chandrasekaran and Barnard, however, uptake occurs predominantly via hair follicles and sweat glands (1).

Schematic view of the three transport routes through the skin: intercellular diffusion, transcellular diffusion, and shunt diffusion via hair follicles

Why the hair follicles are decisive

Hair follicles account for only around 0.1 per cent of the body’s surface area. Their absorptive surface is nonetheless considerable: the deep invaginations of the follicles create a surface many times larger than the smooth skin above them. Because the follicles are not covered by the horny layer, magnesium meets substantially less resistance there. Every cell has transport mechanisms for magnesium, so it can be passed on from cell to cell.

Uptake through the skin is self-limiting: once cells are saturated with magnesium, they take up no more.

Recovery from sweat

To limit magnesium lost through perspiration, the body has cells that actively recover magnesium from sweat. The same cells are able to take up magnesium supplied from outside.

The principle resembles the one in the kidney, where specialised cells reclaim magnesium from filtered urine and return it to the circulation. Certain proteins on the cell membrane are held responsible for transcellular transport — a group of proteins with a raised affinity for magnesium ions, binding them and passing them on once a stable equilibrium is reached.

Schematic view of transdermal absorption from the skin surface into the deeper layers of the skin

What determines how much is absorbed

How much magnesium is taken up through the skin is not a fixed quantity. What matters is:

  • the hydration of the skin
  • the size of the area treated
  • the concentration of magnesium on the skin
  • blood flow in the skin
  • the duration of contact

According to the findings of Chandrasekaran and Barnard, uptake rises with the concentration of the solution and with contact time (1).

For what this looks like in practice, see Application. The underlying studies are summarised under Research.

References

  1. Chandrasekaran N., Barnard R.T.: Permeation of topically applied Magnesium ions through human skin is facilitated by hair follicles. Magnesium Research 2016; 29 (2): 35–42