Most seasoned divers know that the best go-to method for keeping your mask clear is plain old saliva. Spitting in your mask may take some getting used to (it’s okay; every diver does it), but there’s no doubt it works. But how? Why do divers spit in their masks? What’s the secret behind spit-clearing your mask?
Why Do Divers Spit in Their Masks?
A scuba mask fogs up when the inside of the lens is at a temperature below the dew point of the air inside the mask. So, water condenses on the inside of the lens. But the explanation doesn’t stop there. The surface of the glass in your mask is potholed with microscopic depressions. Moisture is attracted to this uneven surface and adheres to the front,t causing the fogging. Decreasing the surface tension and creating a moisture film prevents fogging.
So, how does spit help? Saliva acts as a surfactant. Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading. The term surfactant is a blend of the words surface acting agent. As a surfactant, saliva decreases the surface tension of the droplets. The water from the condensation does not mound up as beads or droplets but, instead, breaks to form bigger droplets that roll away into the mask.
Why spit?
Ok, so why use spit? Well, simply because it’s the most conveniently available surfactant, and it works well, too. You could just as easily use shampoo, detergents, toothpaste, soaps, alcohols, or glycerin, all used by divers as a spit alternative to the same effect. You could also purchase manufactured defogging solutions. But spit is free, plentiful, and doesn’t require a wetsuit with pockets to carry around!
Spitting into your mask and rubbing it around stops the droplets of moisture formed by condensation from clinging to and building up on the glass. Instead, the water beads and rolls away, allowing you to see clearly. This is why you may notice a small amount of water in your mask after you dive, despite having it well sealed to your face and not having had to clear your mask. That water would have fogged up your mask had the saliva or defogger not been there to break the surface tension of the condensation droplets.
Conclusion
Simple, no? If you’re still anti-spitting, never fear — there are plenty of other ways to prevent your mask from fogging!
