Dust in lens... again

You cleaned my ZS25 in October of 2018. Everything was great!! Whenever I’m not using it, I keep the camera protected in a plastic bag on a shelf. 2 days ago I was out shooting and I noticed the camera had piece of dust inside the front lens. My question is… after using this camera a lot over several years (and never having a problem) is there a seal or something that shrinks or wears down letting in dust?