Why Do Masks Have Expiration Dates?
A mask’s effectiveness depends on having a good fit. Over time, it is possible for the elastic bands and nose pieces to start to degrade. If the straps and other structural pieces are degraded, the masks will fit less well.
What about filtration? Research has indicated that the filtration effectiveness of expired masks is not much different than new masks. One study found less than a 1% difference in effectiveness between 10-year-old expired N95 masks and brand new masks.
Bottom line: poor mask performance is far more likely to result from wearing a mask improperly than from the fact that the expiry date has passed.
Unfortunately, living in the tropics means that rubber straps will deteriorate much faster than in cooler climates.
So if the rubber band on your masks has lost its elasticity, it will not fit properly and you should throw it out.