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

[Neilwood]

In cold water diving, this is (IMO) sound practice. Losing your mask, or having a major mask leak can be shocking if the water is cold. Dipping your face in the (cold) water before starting the dive prepares you for the shock of cold water hitting your face and reduces the risk of freaking out you lose your mask during the dive. Less risk of freaking out.

Agreed. On one of my check out dives I had the mask removal and replace to do. As soon as the cold water hit my face it caused me to start to hyperventilate which took a bit to get under control. Getting used to the cold water shock when it is in a "safe"situation does help

 

[TMHeimer]

Agreed. On one of my check out dives I had the mask removal and replace to do. As soon as the cold water hit my face it caused me to start to hyperventilate which took a bit to get under control. Getting used to the cold water shock when it is in a "safe"situation does help

Yes, I've seen this happen with students. I never had the problem, being used to swimming in quite cold water--such as in the Orkneys (as you probably know), as well as here in New Scotland.... Can't say cold swimming will help everyone avoid face-cold mask shock, but probably can't hurt-- you know very well what to expect so it's not a shock and breathing isn't affected.

 

[stuartv]

I agree with a previous poster. Any kind of oils on your face can leach over onto the mask glass and then you'll get fogging.

If I roll out of bed and don't wash my face before I go diving, just the skin oils on my face will cause me problems by the end of the day. Natural body oils and definitely stuff like sun block can do it.

I use diluted baby shampoo for defog (and suit lube) and it works extremely well. As long as I remember to wash my face before I go diving.