Mask leakage is one of the least desirable things to have happen to you while you are snorkeling. It can turn a pleasant experience into one of aggravation in a very short period of time. Most of the time this problem is easily corrected. This information is intended as a troubleshooting guide:
THE FIT OF YOUR MASK
If the mask is new and it is your first time using it, the fit of the mask to your face could be the problem. Masks usually have a double seal which creates a wider sealing surface for the mask skirt. This is so they can accommodate a wider variety of facial sizes. There are, however, faces that a standard adult mask skirt may not fit. Narrower faces, children and those with wider facial features may experience leakage from using a standard adult mask. There are masks available with mask skirts that are large or smaller. Children's masks have the smallest skirt, masks designed for women and youths are larger than children's while being smaller than standard skirts. Masks that have wider in their description have skirts that are sized for those persons with larger facial sizes. I strongly urge you to watch the video How To Fit a Snorkeling Mask, which is to the right, as this will show you how a mask should fit properly.
Silicone, rubber or polyvinyl chloride (PVC) are three materials of which mask skirts can be made. Of the three, silicone is the preferred material as this offers the best seal because of it's durability and flexibility. Rubber can degenerate and PVC tends to stiffen up when exposed to cooler water temperatures.
The hair on your head or the hair on your face will be the cause of your mask leaking. If you have a mustache, you can almost guarantee that it is the source of the problem. The mask has to be able to seal along the upper lip and the hair from the mustache can impede its ability to do so. There is a product designed to help with this particular issue called Mask Seal.
Hair from full beards that extends into the sealing surface of the mask can also affect the mask's ability to seal to the face properly. For more on facial hair, be sure to read our article Do You Have a Mustache or Beard.
Thick eyebrows that extend through the seal of the skirt can also be a problem. If you have longer hair or bangs you may find that this can sometimes get caught between the mask skirt and face which will also break the seal.
Where the mask strap is placed on the back of your head can be a factor on whether the mask seals properly. Having it across the crown portion of the head usually distributes the tension of the skirt evenly.
MASK STRAP TENSION
While your first inclination when experiencing leakage is to tighten the strap, loosening it may actually be the correct solution. The tighter the strap is, the less chance the skirt is able to conform to the face because of the reduction of its flexibility.
YOUR SMILE LINES
If you are blessed with deep smile lines, this can also attribute to leakage. Pulling the mask strap a little higher on the back of the head may help with this. This will pull the bottom portion of the skirt a little snugger to the face without having a great affect on the other areas of the skirt.
If your mask is equipped with a purge valve on the bottom of the nose or by the cheek, check this area carefully to make sure that no sand, grit or other stuff is caught up in this area which will affect how it operates. Also make sure that the purge valve itself is not warped from exposure to the heat.
Though not common, a defect in the mask from the manufacturer can be the cause. It is a possibility that you might have a mask that slipped by quality control at the manufacturer.
These are all just some of the reasons that might cause a mask to leak. Some of them are simple adjustments that you can make on your own. Try them out.