Magnesium spray, often marketed as magnesium oil, is a popular topical solution used for muscle relief and mineral absorption. This product is actually a highly concentrated aqueous solution of magnesium chloride salt, not an oil. The immediate, stinging sensation is a widespread complaint, especially when applied to delicate areas. This discomfort is not an allergic reaction but a predictable physical and chemical interaction between the concentrated salt solution and the skin.
The Chemical Reasons for Skin Irritation
The primary cause of the burning sensation is the solution’s high concentration, which creates a powerful osmotic effect on the skin. As a salt dissolved in water, magnesium chloride forms a hypertonic solution. When this concentrated solution sits on the skin, it draws water out of the outermost layer of skin cells, the stratum corneum, to equalize the concentration gradient. This rapid cellular dehydration leads to the stinging or prickly feeling users often describe as a burn.
A secondary factor contributing to irritation is the potential mismatch between the product’s pH and the skin’s natural acidity. Healthy skin maintains an acidic mantle, typically with a pH around 5.5, which is necessary for barrier function. Commercial magnesium chloride solutions can vary, but are often near neutral or slightly higher (around pH 7.5). Applying a solution with a higher pH than the skin’s natural surface can temporarily disrupt the protective acidic mantle, making the skin more vulnerable to irritation from the salt.
The feeling of irritation may also be intensified by the residual salt left on the skin after the water evaporates. This salt residue can be physically irritating, especially as it crystallizes on the surface. Furthermore, the positively charged magnesium ions move rapidly across the skin barrier, a process perceived as an intense tingling or stinging sensation.
Why Armpits React More Strongly
The skin of the armpit, or axilla, is uniquely predisposed to react more intensely to the concentrated salt solution than other areas like the legs or back. The skin in this region is naturally thinner than that on most other parts of the body, which already makes it more sensitive to topical applications. This area is also considered an occluded site because the skin folds over itself, trapping heat and moisture, which significantly increases the rate of transdermal absorption.
The armpit is densely populated with hair follicles and sweat glands. Hair follicles serve as a direct, deep pathway into the skin layers, allowing magnesium ions to bypass the protective surface layers more easily. This increased pathway availability means the concentrated solution penetrates deeper and faster, leading to a more pronounced stinging sensation.
Regular shaving is a major contributor to the burning sensation. Shaving causes micro-abrasions and tiny, invisible cuts in the stratum corneum, damaging the skin’s barrier function. When the magnesium chloride solution is applied, the salt directly contacts and irritates these compromised areas, similar to the sting of salt water on an open wound. The combination of thinner skin, frequent barrier compromise from shaving, and the occlusive environment makes the armpit highly reactive to magnesium spray.
Practical Steps to Stop the Burning
You can significantly reduce or eliminate the burning sensation by adjusting how and when you apply the magnesium solution. Start by diluting the spray with water to lower its concentration and reduce the harsh osmotic effect on your skin. A common starting point is a 1:1 ratio of magnesium spray to water, and you can gradually increase the magnesium concentration as your skin adjusts.
Timing your application is also important, particularly in relation to hair removal. Wait at least several hours after shaving, waxing, or exfoliating the armpit area to allow micro-abrasions to begin healing before applying the spray. Applying the solution before a shower or bath is another effective strategy; you can rinse it off after 20 to 30 minutes to wash away the irritating salt residue.
If the armpit remains too sensitive, consider switching to less reactive areas, such as the soles of the feet or the legs. These areas have thicker skin and fewer sensitive pathways, often allowing for topical application without discomfort. After rinsing the solution, applying a soothing moisturizer can help restore the skin’s barrier function and rehydrate the area, counteracting the salt’s dehydrating effect. If the burning is severe, accompanied by a rash, or persists, discontinue use or consult a dermatologist.