Swimming in salt water won't make you gain weight. Your skin acts as a barrier that prevents water absorption, as well as absorption of chemicals such as sodium. The outermost layer does absorb water, which is why skin wrinkles in water, but this is a short-term effect. Although salt does retain fluid, salt water on your skin will not penetrate through the layers deep enough to increase fluid retention and weight gain.
Absorption in the Stratum Corneum
The epidermis, the outer layer of skin that you can see, is actually comprised of dead cells. The top layer, called the stratum corneum, does absorb small amounts of water. The bottoms of the feet, the palms and fingertips are most affected because the stratum corneum is thickest in those areas.
The Role of Sebum
The layer beneath the epidermis, called the dermis, contains sebaceous glands, which lubricate the skin. Sebaceous glands produce a substance called sebum, which acts as a natural barrier to protect your skin from absorbing water or other foreign substances further into the tissues.
Salt and Fluid Absorption
When you ingest high levels of sodium, one of the two ingredients in table salt, you may retain fluid. But salt on the outside of your skin does not have the same effect. If anything, salt on your skin would pull moisture out of the skin, but this does not happen, as the dermis holds the fluid in.
Considerations
Even if you gain a small amount of weight from fluid absorption into the stratum corneum, the effect doesn't last long. As soon as your skin begins to dry, the excess fluid evaporates. Some websites claim that saltwater pools and water softeners that use salt can increase your absorption of sodium and chloride, but they offer no clinical evidence of this. Retired general internist, author and health columnist Dr. Peter Gott states that water softeners do not add a significant amount of sodium intake, even when you drink the softened water, much less bathe in it.
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