A common concern when swimming in a saltwater pool is whether the body absorbs sodium, potentially affecting internal salt balance or blood pressure. Systemic absorption of sodium through the skin from a standard saltwater pool is negligible and does not meaningfully contribute to the body’s internal sodium levels. This lack of absorption is due to the pool’s low salinity, the robust barrier function of human skin, and biophysical movement principles.
Understanding Saltwater Pool Chemistry
A saltwater pool is a misnomer; the water is not the same as ocean water, which has a salinity of approximately 35,000 parts per million (ppm). Residential saltwater pools typically maintain a salinity level between 3,000 and 6,000 ppm, closer to a weak saline solution. The primary purpose of adding sodium chloride salt is not to create a high-salinity environment but to feed a chlorine generator.
This device uses the salt to produce a consistent, low level of chlorine gas through electrolysis. The resulting water is often described as feeling softer or silkier than traditional chlorinated water, which is a major factor in their popularity. The salt concentration is so low that it is only about one-tenth the concentration of the ocean.
The Skin Barrier and Non-Absorption
The skin acts as a biological barrier, designed to protect the internal environment from the external world. The outermost layer, the stratum corneum, is the primary defense against the passive entry of external substances, including sodium ions. This layer is often described as a “brick-and-mortar” structure, where flattened, dead cells (corneocytes) are held together by a lipid-rich matrix.
This highly organized structure, composed of ceramides, cholesterol, and fatty acids, creates a hydrophobic environment that resists the passage of water-soluble ions. The sodium ion (Na+), being a charged particle, is poorly suited to pass through this lipid matrix. The skin is semi-permeable, designed to keep water inside the body and large molecules and ions out, preventing systemic absorption of pool salt.
Concentration Gradients and Osmotic Pressure
The movement of solutes like salt across a barrier is governed by concentration gradients and osmotic pressure. Internal body fluids, such as blood, have a salt concentration of approximately 0.8% to 0.9% (8,000 to 9,000 ppm). Since a saltwater pool’s salinity is much lower (3,000 to 6,000 ppm), the water is considered hypotonic relative to the body’s cells.
This concentration difference means there is no significant gradient driving sodium ions from the pool water inward to the bloodstream. If any osmotic exchange occurs, the gradient favors a slight net movement of water out of the skin, not salt into the body. The skin’s barrier function prevents meaningful exchange from affecting internal fluid balance, though the osmotic difference can contribute to a subtle effect on surface moisture.
Topical Effects on the Skin
While systemic absorption of sodium is prevented, the salt water does have localized, topical effects on the skin. The most notable consequence is a temporary sensation of dryness or tightness after swimming. This feeling is caused by residual salt and water on the skin’s surface evaporating into the air.
As the water evaporates, it leaves behind salt crystals on the outer layer, which can draw moisture out of the stratum corneum. For individuals with a compromised skin barrier, such as those with eczema, this localized osmotic effect can lead to mild irritation. Rinsing with fresh water immediately after exiting the pool is the most effective way to remove the salt residue and prevent drying effects.