Your mask will be covered with proteins from your skin and from the ocean water. These will be embedded in oils from your skin or in sunscreen, etc. and will not rinse easily. There's no real problem, but I have one word of advice: if you store your mask in a plastic box or anything air tight, make sure the mask is thoroughly dry before putting away. If it is not really, truly dry, you run a high risk of growing a fungus colony on those proteins. It happened to my wife's prescription mask. I had to kill the colony with bleach, then get rid of the residue with hydrogen peroxide. The mold grows in any crease or corner where there might be enough moisture to sustain it. In my wife's mask, that meant the mold grew in the tight spaces all around the edges of her lenses, places into which I couldn't even stick the end of a toothpick. Dry before storing in that cool, dark location.