The sting is salt. The serum level is a different door.

Magnesium oil is a concentrated solution of magnesium chloride, sometimes with colour and fragrance, and it stings on the skin because salt and osmolarity irritate the surface. The word oil is a sales habit. The market has turned that sting into a sign that the mineral is soaking in. What the stratum corneum does with a divalent ion is narrower. Charged, hydrophilic particles cross lipid lamellae poorly. The route that reliably raises serum magnesium, when intake is low or a deficit is present, remains the mouth. The spray after training keeps a different job: a ritual on the skin, sometimes a massage, sometimes an itch at midnight. On the Fitnessmarkt floor the bottles are demonstrated on warm skin straight off a bike, which is exactly the skin most likely to sting and least likely to prove a serum change.

Why Mg2+ stalls in the stratum corneum

The stratum corneum is the barrier at which most transdermal ideas stall before an active sees living epidermis. Magnesium ions are small, and they are charged and wrapped in a hydration shell. Partition into the lipid-rich matrix is unfavourable. The ion would rather stay with water. Follicles can offer a side path, quantitatively small against the surface area, and they are exactly where concentrated salt solutions provoke a folliculitis-like irritation. The prickle along a hair follicle is a clue. It is a poor receipt.

Damaged skin, fresh abrasions and mucosa are more permeable. That is a reason to keep the spray off those sites. An athlete with split hands after pull-ups feels more sting and has a locally different barrier. Building a dose recommendation for intact skin out of that observation turns the exception into the method. Intact skin is the skin the bottle claims to serve.

Studies of foot baths with magnesium sulphate, of sprays and of float tanks are heterogeneous, often small, rarely with clean control of diet, sweat loss and baseline. Individual papers report shifts in serum or urine. Others find no robust rise. For this desk that picture is too uneven to tell a team the spray replaces intake. It is enough to say the skin route has not been established as reliable substitution. Serum magnesium itself is a sluggish marker, because most of the body store sits inside cells. A normal serum value does not, in every case, exclude a tight supply. A single low value belongs in medical hands. Erythrocyte magnesium is sometimes measured in sports practice as well. That measurement still leaves an indicated oral dose where the indication put it.

What is evidenced by mouth

Several salts are available orally: citrate, glycinate, oxide, with different solubility and a different tendency to diarrhoea at a higher dose. Where intake is documented as low, supplementation can support the store. That is nutrition and medical practice, dependent on kidney function and on medication. A clinic does not sell that decision beside the shoes, between a foam roller and a playlist. The person qualified to dose it is the person who can see the kidney and the drugs.

Evidence for muscle cramps in older adults without a clear deficit is weak. A Cochrane review finds no reliable benefit of magnesium against those cramps. Athletes with night-time calf cramps often have training load, salt, sleep and fluid as the larger levers. A spray that promises cramp protection takes on a claim that even the oral dose does not carry cleanly. The calf at 2 a.m. has several authors. The bottle is the loudest and the least evidenced.

Recovery after load hangs on sleep, on the next meal, on the size of the load itself. A massage oil that contains magnesium can feel pleasant because hands, warmth and a ritual lower tone subjectively. That feeling is real. It is touch and expectation. Placebo is the correct description of an effect that runs through those, while a serum rise from the spray has not been shown. The word is precise. It is not an insult to the hour on the mat.

Sting on the skin is osmosis and irritation. Anyone who wants the level raised calculates the oral dose and the kidney. The spray bottle keeps a different ledger.

Sweat loses sodium first

Sweat loses water and sodium first, plus smaller amounts of other electrolytes, magnesium among them. The concentration of magnesium in sweat is low beside sodium. Trying to put that loss back in through the skin runs against the barrier at its strongest property. Food and, where needed, an oral preparation at a dose that can be agreed replace what the sweat took. A salt mark on a jersey is mostly sodium and water. It is a poor portrait of a magnesium hole the size a spray dramatically closes.

After training the skin is often warm, damp and already mildly irritated. Spraying a concentrated chloride solution onto it increases the sting and can disturb sleep when it itches. A house that wants to keep the ritual separates massage from substitution. The massage can stay, with a low-fragrance oil if the skin is already angry. The substitution is labelled for what the mouth can do. Fitnessmarkt demos that rub the solution in during the cooldown and then talk about replacing what was sweated have joined two ledgers. Sodium and water dominate the sweat ledger. Magnesium is a smaller line on the same page.

Interactions are the point at which cosmetics stop. Renal insufficiency, certain diuretics, an oral dose that is already high: more magnesium is then a medical question, whichever route someone imagines for it. The cabin does not take a kidney history the way a practice does, and for that reason it promises no correction of the level. A pleasant oil on the calf is allowed to be a pleasant oil.

What a performance studio can write down

A recovery protocol records sleep time, the last meal, subjective heaviness, and next-day soreness, on a simple scale. If an oil is used, it is used as an oil, with ingredients that suit the skin, low in fragrance when the skin is already irritated. Magnesium chloride may be in it. The protocol stops short of claiming the muscle has been supplied. The feeling in the room can be logged. The serum stays out of the sentence.

For athletes with frequent cramps, or with very low energy availability, the useful service is a referral: medical or sports-medicine review, a nutrition check. A larger bottle is a larger bottle. Sodium loss in long endurance sweat is, in many cases, the closer electrolyte lever, and it is not self-medication off a shelf either. The study picture can be one sentence in the conversation. Skin takes up magnesium ions poorly. Oral intake is the evidenced route for supply when supply is the question. Cramp protection is uncertain even by mouth. The sting is irritation with a good publicist. A seller who dislikes that sentence is selling a different product. This desk stays with the sentence, because the stratum corneum is not persuaded by a label. The supplier demo can show the texture. The serum question is answered before the bottle is wrapped, while the skin is still warm and the claim is still trying to catch a ride.