​Perhaps, because most new dive masks have mold release agents in the flexible skirt that are volatile and during storage will migrate to the surface of the lens to cause fogging. This is often the case when the mask has been sealed in an air-tight box or plastic bag. These deposits can be safely removed with an extra application of a powerful non-abrasive surfactant like liquid dish soap, baby shampoo, SeaQuick or SeaDrops defog.

The mask may persistently fog at first, requiring repeated cleaning, but with the passage of time the mold release agents will dissipate naturally and the issue will resolve itself. To hasten the dissipation of the mold release agents from the mask silicone, store the mask so that it is exposed to air between dive trips and use a sealed box only for transport in the dive bag. Do NOT let the mask get hot during transport, i.e. keep your bag and mask box out of the sun.

Don't use toothpaste or any other other abrasive on modern dive masks, especially those masks that have optical quality ultra-clear glass lenses, vision correction lenses or 'optical coatings' on the lenses. You will either damage the lenses, or needlessly waste toothpaste since many modern toothpaste formulations are not at all abrasive.