Application

Dosage forms

Three forms are mainly used for application through the skin. They differ less in principle than in their magnesium content.

Liquid solution (spray or “oil”). A saturated magnesium chloride solution in water, at around 31 per cent. “Oil” here describes only the oily feel on the skin — the solution has nothing to do with fat. It is applied directly to the skin as a spray.

Gel. The same magnesium chloride solution, thickened with a gelling agent. It can be massaged in and stays in place longer; its magnesium content is lower than that of the concentrated solution.

Bath flakes. The solid form, magnesium chloride hexahydrate. The flakes dissolve in warm water and are used for full and foot baths (see below). Of the three forms they have the highest magnesium content.

How much elemental magnesium is in them? What counts is not the amount of solution but the proportion of pure — “elemental” — magnesium:

• Liquid solution: 1 millilitre of the saturated 31 per cent solution contains around 103 mg of elemental magnesium.
• Bath flakes: 1 gram of flakes contains around 120 mg of elemental magnesium.

The derivation: magnesium chloride has a molar mass of 95.2, magnesium one of 24.3 — so about 24.3 / 95.2 ≈ 26 per cent of the mass of magnesium chloride is pure magnesium. One litre of the saturated solution contains around 403 grams of magnesium chloride, one kilogram of flakes around 470 grams. The two figures above follow from that.

Magnesium for daily use

For daily use, the magnesium solution is applied to the skin and massaged in. The usual approach is about 2 millilitres morning and evening; that corresponds to roughly 400 milligrams of elemental magnesium in the applied solution (which says nothing about how much is absorbed).

For daily use, the arms and shoulders have proved practical: they are easy to reach, and the concentrated magnesium chloride solution is generally well tolerated there. Thighs, lower legs or the abdomen also work. The underarm area is an option too — there are many sweat glands there, and sweat glands and hair follicles are discussed in the research as possible transport routes.

How many sprays or drops are needed depends on the concentration of the solution and on how many sprays make up 1 millilitre of the product in question. Depending on the product, the recommendation falls between 5 and 20 sprays per application. A precise target amount cannot be given responsibly, since the amount absorbed through the skin has not been scientifically established.

Full baths and foot baths

Baths are usually prepared with magnesium bath flakes; the liquid solution can in principle be used as well.

Full bath. What matters is the magnesium concentration, the body surface covered by water, and the temperature and duration of the bath. Water temperature should be around 37 degrees Celsius, and the bath should not be shorter than 20 minutes. For a normal-sized bathtub, roughly 500 to 1,000 grams of bath flakes are used.

Foot bath. The practical and cheaper alternative. Because the body surface covered is considerably smaller, the concentration should be higher — between 2 and 5 per cent. The feet should be covered above the ankles, the temperature again around 37 degrees Celsius, and the contact time at least 20 minutes.

When oral intake is difficult

As far as absorption in the gut is concerned, magnesium is not a straightforward substance. Even an intact gut with a healthy flora takes up only part of the magnesium supplied — figures in the region of 30 per cent are cited in the literature. Absorptive capacity also changes over the course of a lifetime.

Some people therefore deliberately go without additional magnesium, because even small doses lead to discomfort, bloating or diarrhoea. External application does not involve the digestive tract — for this group, that is the decisive difference.

In later life there is a further factor: stomach acid production declines. Stomach acid is involved in converting magnesium into a form the body can absorb. That too explains why external application attracts interest in this group.

Sport and physical exertion

Physical exertion raises the magnesium requirement, and minerals are additionally lost through sweat. Magnesium contributes to normal muscle function, to normal energy-yielding metabolism and to the reduction of tiredness and fatigue — these authorised statements refer to the magnesium supplied through the diet, not to external application. External application can be combined with oral intake.

Pregnancy and breastfeeding

Magnesium requirements are raised during pregnancy and breastfeeding. External application is sometimes chosen in this group because it does not involve the digestive tract.

Important: if you are pregnant or breastfeeding, discuss magnesium intake with your doctor or midwife. That applies to external application just as much as to oral intake. Questions about your own nutritional status can only be answered individually, with knowledge of your state of health — not by a website.