Tuesday January 28 2020
June 25, 2013

Why Do We Spit Into Our Dive Masks?

Last Sunday, I was preparing one of my dive students for try scuba diving program. In my briefing, I told her about everything she is going to need underwater, with “do”s and “don’t”s like I did hundreds of times in my dive career. We were almost ready to go. Lastly, I have wanted her to spit into her dive mask in order to prevent the fog during the dive. She asked: “Why?” I repeated my last sentence: “to prevent the fog during the dive, take it as a pre-caution” I then realized that this wasn’t the question. She said “I didn’t mean it. How can spitting into a dive mask can prevent fog, what is happening there?”

Although there are some commercial “mask defoggers” being sold, we are generally using our own spit to get rid of fogging. Thousands of divers around the world is doing the very same thing before each dive. We spit into our dive masks, rub the lenses and the silicone parts with it and rinse our masks with the sea water. But how many of us know the answer of this question that my try scuba diver candidate has asked?

I know spitting seems to be disgusting, but none of the divers want to ruin their dives just because of a damn dive mask fog. Yes, if you don’t have a mask defogger solution, you should spit into your dive mask and rub it with your finger. Then you can rinse your mask with sea water and start to enjoy your dive. This is one of the best moments in my pre-dive briefings in try scuba diving and open water diver courses. Imagine an elegant female diver who is about to dive. She even has a little bit of make up and looking good with her stylish pink dive suit. And you are telling that she should spit into her dive mask now! Ohhh, no!!!

Let’s turn back to our topic. To be able to understand how our spit is helping do defog our masks, we should know about the reasons of fogging first.

What Is Fogging?

Imagine your self taking an ice cold cola bottle from your fridge. When you pour cola from its bottle to a random glass, you can see some droplets outside of the glass. These droplets become more visible and more in number if it is especially summer. You also see what? Some obvious fog on the glass. It looks like the glass is “sweating”.

It has the exact logic with raining. As we all know from the elementary school, water evaporates when there is enough heat and rises to the sky. When it “meets” with a cold air layer, it condenses and falls to Earth as rain.

And when you pour cold cola in your glass, inside layer of the glass is getting colder. But the outside layer and the room is warm. There is always humidity (moisture) in the air.  When humidity “crashes” your ice cold cola glass, it condenses. The result is fog and droplets.

Why My Dive Mask Is Fogging?

When you are underwater, the outer glass of your dive mask lens is getting colder, but inside is warmer due to your face temperature and breath. The heat is coming from these two. And you are also exhaling. There is  humidity in your breath. When warm air and humidity meets and crashes with a cold layer, result is a foggy mask! So you have also learnt that in winter, “fogging mask” problem is often compared to summer.

If we go a little bit more specific, I can tell you that water’s chemical structure is interesting. Water molecules can “link arms” with each other, which is called “surface tension”. You exhale, humidity in your breath and warmth of your face “crashes” to the cold outside glass of your mask. Condensation occurs and water molecules grab each other. This is the reason of the “dive mask fogging”. Think the fog on your dive mask as tiny water molecules holding each other and making a ring (also called surface tension).

How to Defog My Dive Mask?

You simply spit into your dive mask. Spit is something legendary in this point. It gets between the water molecules and prevent them to “hold” each other. Water molecules cannot form a ring by linking each other. This is what we call “reducing the surface tension”.

When the surface tension is reduced (when you spit into your dive mask and water molecules loose their ability to grab each other and spread), water molecules can only form bigger droplets. That’s because they have to go to edges of your mask and get collected there. More water molecules mean bigger droplets.

This is why even if you don’t remove your mask underwater, there collects a few drops of water when you surface (this is fresh water, came as humidity from your lungs).

You can also use mask defoggers. These act just like spit and prevents the water molecules to hold each other. Even I have seen small piece of plastic that you attach to your outer mask lens. This piece of plastic keeps the outer lens warm and works as a defogger. You can check it out in Amazon.

What If I Have a New Dive Mask Fogging?

Yes, I know that your brand new dive mask that you have enjoyed buying is fogging. Even in your first dive after your purchase!! You are lucky that every mask on the world can be defogged, but some may need extra attention. New dive masks do fog, because some small particles stay in your mask after the production process in the factory. These small particles absorbs heat and increases the fogging possibility. First, we should remove these residue from our masks.

Use a Toothpaste

Right after you have bought your mask (if you have missed this and dived with your mask already, also try this method), you are taking a toothpaste (be careful not to have some granules in the toothpaste that might damage your lens) and last it to your index and middle fingers. Now you can rub inside your new dive mask. Everywhere, silicone and the lenses. Small fabrication particles especially get collected in your mask’s nose pit. Make the nose pit come out with your fingers and toothpaste there well. With all the toothpaste in your mask, let it stay like that for one day. Then rinse it with fresh water.


Another technique for removing the production particles is to burn them. Yes, I am not kidding. Take a Zippo or a candle and let the flames suck inside your mask. The flames should only suck your lens! Do this until your lens gets black. Black lens means “burning fabrication particles”.  When your lens become all black, stop the fire and remove this “blackness” by using a soft towel.

Repeat this process few times more until your lens doesn’t turn into black. When the lens doesn’t get black, you can be sure that there is no residue on your lens anymore. You can go on just using your spit or a mask defogger solution after this.

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About Seaman


Hi, my name is Murat Demirağ. I have been diving since 1996 and teaching scuba since 2005. I wanted to share my knowledge through divewithseaman.com

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