How to stop a snorkel mask from fogging

Why masks fog

Inside a mask the air is warm and humid: it touches your skin and, if you breathe out through your nose, it carries your breath. The lens is cooled by the water outside. When warm, moist air meets a cooler surface, the moisture condenses into droplets too small to see one by one, and the lens turns milky. U.S. Divers calls this “a normal occurrence”^[1].

The second cause is specific to new masks with glass lenses. During manufacturing, the maker explains, “a thin film of silicone will develop on the glass lens. This film of silicone will cause rapid fogging that is resistant to conventional anti-fog measures”^[1]. Droplets cling to that film instead of spreading out into a clear layer.

Fix it in this order

1. Remove the factory film (new glass lenses only)

U.S. Divers’ instruction for its masks is to scrub the lens inside and out with a mild abrasive before the first use: “A paste toothpaste is ideal but a liquid scrub will also work. Rub the cleanser into the lens with your fingers several times and then rinse clean thoroughly”^[1]. Use a plain paste, not a gel or whitening formula with grit, and rinse until no residue is left.

Do this only on glass lenses and only if your mask’s instructions allow it. Many full-face masks and some traditional masks have plastic lenses that an abrasive can scratch. If your mask is plastic or you are not sure, follow the maker’s own cleaning instructions.

2. Use an anti-fog product before every swim

Hawaii’s ocean safety page puts it in its equipment checklist: “Use an anti-fog product in your mask before you get in the water”^[2]. Apply it to the inside of the dry lens, spread it, and rinse lightly if the product says so. U.S. Divers mentions saliva as an alternative for normal fogging^[1].

Read the label first. U.S. Divers warns that “some after-market anti-fog agents contain formaldehyde, alcohol, or other substances that may damage the plastic materials used in your mask”, and advises avoiding prolonged contact between the anti-fog agent and plastic parts if you are unsure^[1].

3. Keep the inside clean and dry until you go in

Fingerprints, sunscreen and skin oil give droplets something to cling to. Put the mask on just before you enter the water, keep sunscreen off your forehead where the skirt sits, and avoid touching the inside of the lens.

4. Stop the leaks

A mask that lets water in also brings in cold and splashes, and constant clearing smears the lens. Hawaii asks that your mask “fits properly and does not leak”^[2]. U.S. Divers notes that a mask cinched too tightly can lift at the sides; loosen the straps until it is snug without lifting^[1]. The seal test shows where a leak comes from.

If it fogs during a snorkel

Swim to a place where you can stand or rest safely, near your buddy, before you sort it out. U.S. Divers suggests carefully removing the mask and spreading saliva over the lens with a finger^[1]. If water gets into a traditional mask, DAN describes how to clear it by breathing out through your nose while tilting your face up and lifting the lower edge of the mask slightly^[4].

Full-face masks and fog

Full-face masks are designed to send your breath through a separate nose-and-mouth chamber so the main lens stays clearer. One maker’s FAQ says its mask “should not fog” and needs “no product treatment” thanks to its airflow design^[3]. Take that as the maker’s statement for its own model, and use only the cleaning and anti-fog products its instructions allow. If a full-face mask fogs or you feel uncomfortable in it, get to a place where you can stand and take it off; do not try to fix it in deep water. Our full-face safety guide covers what to watch for.

After the swim

Rinse the mask in fresh water, let it dry out of the sun and store it in its case. U.S. Divers advises soaking in warm fresh water no hotter than 120°F to dissolve salt, and storing gear in a cool, dry place away from heat and direct sunlight^[1]. A clean lens fogs less next time.