What causes mask fog (and how to stop it)?

[SharkEsq]

So I just got back from 3 days of diving in Phuket, and had a strange experience. I've got a somewhat new mask that I had properly treated (i.e. a DM took his lighter to it for a while when I was in Key Largo) and hadn't had any issues with it before (over maybe 20 dives). But on this trip, I had about 3 of my 10 dives where I was regularly having to flood and clear my mask to get rid of the fog. But on my other dives, it was fine and didn't fog at all.

I used two different defogging agents (J&J baby shampoo for some, and mystery juice in the boat's squirt bottle for others) and I had mixed experience with both. The surface and bottom temps were pretty consistent on all my dives. Does anyone have any idea what causes the fogging, and why it happened on some of my dives but not others? Is there a proper way to apply the defog soap (i.e. rub it in hard, or not? leave a little on or wash it off really well?)? Something else that might be the difference?

 

[Diving Dubai]

From personal experience.

I use baby shampoo, and make sure the glass is dry before application. Just a thin smear and let is rest (but not dry) I used to give it a quick rinse with fresh water, (when you rinse you want to make sure theres no bubbles in your mask fro the soap, but not was it completely off) occasionally I'd still get some fogging.

Now I rinse with sea water (after applying the baby shampoo) and have never had a fog since. There must be a scientific explanation but I don't know it.

- hope that helps

 

[CuzzA]

The key to a fog less mask is cleanliness. Flaming or using tooth paste removes the initial residue from the manufacturing process. As you continue to use the mask oils from your skin and other bio funk builds this residue layer back up which causes a mask to fog.

Here's what I do. Flame the mask or toothpaste it and then clean it with some Dawn or anti bacterial hand soap. Then I will apply a thin coat of defog and let it dry over night or until my next dive. Before I splash I will rinse the mask with a little fresh water to remove the defog streaks and I can dive the whole day without reapplying any defog. At the end of the day I will again clean my mask really well with Dawn or antibacterial hand soap, dry it and then reapply defog and store the mask until my next day of diving. Eventually after a year or so I will re flame the mask or toothpaste it to remove any residual bio funk build up.

So far I've yet to have a mask fog on me.

 

[Alastor]

One of the worse fogging substance is sunscreen - avoid it, because it perspires from the skin and has a fat component which settles on the glass and facilitate fogging. Just in case your skin is so sensitive you have to protect it, rinse very well your face, rubbing vigorously before wearing the mask - you do not need the protection while diving - then you can apply it again at the surface (or stay in the shadow before diving).
As others told you, defogging should not be dry when you enter the water - any surfactant will do - from saliva (spit - forgive me I'm not mother tongue) through soap - baby shampoo is used because would not irritate eyes.
You can also spread it with the finger over the whole inner glass surface, a small quantity is enough.

 

[Neilwood]

I would guess that perspiration might be the issue.

If I feel hot before a dive I will tend to splash, slip my mask off or onto my forehead, dip my face in the water to cool down, quick wipe with my hand to minimise the water on my face and then replace the mask.

Having said that, I find spit to be one of the best de-fogs available. I have never run out.

 

[TMHeimer]

My baby shampoo method:
A dab on each mask lense. Wipe clear with toilet paper (small lengths of TP--you will have to do this maybe 3 times). You can do this days prior to the dive (or maybe longer). It will probably streak a bit when gearing up with mask on. A little water on the (inside of course) glass prior to descending cures that.
Some people "burn" their mask, though I still am leery on trying that. I'm the one who will ruin the skirting.

 

[nolatom]

What I (an English major) think causes fog is the mask glass being cooled by the water, while your forehead and nose remain at skin temperature of what, about 90F?
So water vapor in the mask, warmed by your face, cools against the inside of the glass, condenses, and deposits that liquid mist, namely, fog, onto the glass.

I defer to scientists on this, and to everyone else about all that other stuff..

 

[Alastor]

Glass temperature will be always lower than skin - you would have some problem in the other way around.
Fog is composed of a myriad of small drop that are kept separated by an idro-repellent substance on the glass: grease, silicone from factory or other idro-repellent substances.
When you want to get rid of that drops, usually you flood the mask and the drops connects and collapse into a thin layer ... till they will be separate again ... and if there is any idro-repellent substance, they will appear very soon.
The purpose of any surfactant is to ease the drop aggregation - this is why, for example, till the glass is wet, you have no fog.
Burning the mask has the purpose to get rid of the thin silicone layer every mask has on the glass - just because the way they are built - that layer is very difficult to remove by abrasion - and the risk to scratch the glass is real.

 

[JamesBon92007]

Having said that, I find spit to be one of the best de-fogs available. I have never run out.

I ran out of spit years ago. At least, it always used to work and now it doesn't seem to any more. Except for the bottle of commercial "Spit" that I bought many years ago--I still have plenty of that and it still works.

I'm at a loss as to how someone can plan days in advance to apply de-fog--every dive boat I've even been on does at least two dives.

What causes fog? I'd always thought it was from exhaling through the nose, but if that was the case my mask would probably always be fogged up because I clear my mask automatically. Occasionally it will fog up on a dive so I let in a little water and swish it around. The next thing I know the water is gone and sometimes I need to let some in again. I sure don't think about it, it just happens. Whenever it does fog up it seems to coincide with not using any de-fog solution beforehand. On a recent trip I didn't have my bottle of "Spit" with me so I used some kind of liquid detergent they had on board. Whichever solution I'm using, I just put a very small dab on my finger, rub it around on the glass, and rinse it gently. That always seems to work. So far nothing has irritated my eyes. Some of the things I've had success with are: Colgate Dish Detergent, Spit (possibly no longer available), Dawn Dish Detergent, Soap Bubble Solution (for blowing bubbles), Some kind of Mexican liquid detergent, and, of course, Baby Shampoo. I have some reservations about soaking my mask in the bucket of whateveritis on dive boats because it may not have antibacterial qualities and I fear it could spread eye, skin, or nose infections.

 

[TMHeimer]

Spit varies. Mine not so good.