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New study shows how sweat really forms

If you're currently experiencing a hot summer, the chances are the sweat is pouring off you, soaking your clothing. This clear, odorless substance is a vital component of a healthy bodily function that helps cool you down and prevent overheating. However, the process by which sweat forms and emerges from the skin is more intricate than previously thought.

Sweat may often appear as a series of discrete droplets seeping from the skin, but a new in the Journal of the Royal Society Interface tells a different story. Instead of forming distinct beads, sweat rises like a tide through the pores to saturate the top layer of skin. It gathers in a shallow pool in each pore before merging with others to form a complete film across the skin's surface.

"Our findings challenge the traditional conceptualization of sweat emerging from pores as hemispherical droplets, demonstrating that sweat commonly forms a shallow meniscus in the pore," wrote Konrad Rykaczewski, the study's corresponding author. This is why it doesn't take long for a T-shirt to become drenched on a sweltering day.

Understanding the sweat process

We don't fully understand how sweat forms, spreads and evaporates, from a single pore to covering the skin. Previous studies employed separate methods to understand what was happening at the pore level (microscale) and larger skin regions (macroscale). This new research combined both approaches.

Making volunteers sweat

Scientists recruited six healthy adult volunteers and basically watched them sweat. Each participant relaxed in a recliner, wearing a specialized suit filled with tubes that circulated warm or cool water. They were also wrapped in heated blankets, with a waterproof paper layer in between to keep the blankets dry.

The subjects were heated, cooled, then heated again while researchers measured the sweat forming on their foreheads. They began to perspire within 15 minutes, with sweat emerging and evaporating from their pores in a repeating cycle. Instead of forming little droplets, the sweat was nearly flat, settling in each pore until it spilled out and connected with sweat from other pores to create a puddle, which then formed a film coating the skin.

The sweat soaked through the outermost layer of dead skin cells (stratum corneum), and once it was completely soaked, the sweat pooled on top. When the participants were cooled down, the newly formed film of sweat rapidly evaporated, leaving behind a thin layer of salt.

After heating the participants again, the sweat emerged quicker than before. This time, the salt layer allowed the sweat to soak more quickly into the stratum corneum, and the second sweat layer bypassed the droplet stage entirely, emerging as a film.

Understanding the ins and outs of sweating has broad implications for everyone, from elite athletes on a race track to workers trying to beat the heat in a stuffy office. It could lead to better products and textiles for managing sweat and maintaining healthy skin.