The human body does not absorb significant amounts of salt, such as sodium chloride, through intact skin. The skin acts as a highly effective barrier, preventing most external substances from entering the bloodstream.
The Skin’s Protective Role
The skin functions as a protective barrier, shielding the body from the external environment. Its outermost layer, the epidermis, is primarily responsible for this defense. The stratum corneum, the outermost part of the epidermis, forms a robust “bricks and mortar” structure. This layer consists of flattened, dead skin cells (corneocytes) embedded in a lipid-rich matrix, which collectively create a formidable barrier against the passage of most substances, including charged ions like salt.
How Substances Pass Through Skin
Substances can attempt to cross the skin primarily via passive diffusion directly through the stratum corneum, or to a much lesser extent, through skin appendages like hair follicles and sweat glands. The stratum corneum is composed largely of lipids, making it challenging for water-soluble and charged molecules, such as salt ions, to penetrate. While hair follicles and sweat glands offer potential pathways, their contribution to absorption is very limited, meaning salt ions do not readily cross the skin’s primary lipid-rich barrier.
Salt Absorption in Different Scenarios
When bathing in saltwater, such as in the ocean or with bath salts, sodium chloride (table salt) is not significantly absorbed by the body through intact skin. While skin might feel dry or “salty” after swimming in the ocean, this sensation results from water loss from the skin due to osmosis and surface salt residue, not from salt entering the bloodstream. The body tends to lose water to the higher salt concentration in the surrounding environment.
Epsom salts, chemically known as magnesium sulfate, differ from common table salt. Some research suggests that magnesium and sulfate ions from Epsom salt baths might be absorbed to a limited degree. Studies have reported increases in blood and urinary magnesium levels after soaking in Epsom salt solutions, though the extent and clinical significance of this absorption are still debated. However, even with potential absorption, it is generally not substantial enough to impact systemic electrolyte balance in healthy individuals.
Damaged skin presents an exception to the skin’s usual impermeability. In cases of severe burns or open wounds, the skin’s protective barrier is compromised, allowing for some absorption of external substances, including salts. This highlights the importance of the intact skin barrier in preventing significant entry of compounds into the body.
Maintaining the Body’s Salt Balance
The human body possesses internal systems to regulate its salt and fluid balance. The kidneys play a central role, controlling the excretion and reabsorption of sodium and water to maintain appropriate concentrations in the blood and extracellular fluid. Hormones such as aldosterone and vasopressin are integral to this regulation. Aldosterone influences sodium retention in the kidneys, while vasopressin primarily controls water reabsorption. These regulatory mechanisms ensure that any minimal absorption of salt through intact skin does not lead to an electrolyte imbalance in healthy individuals.