Have you ever wondered what a smell is? It's a collection of microscopic "stuff" (well, molecules) floating through the air, that enter your nose, hit your olfactory neurons in your nasal passages and transmit a message to your brain, which you perceive as "smell". Where do these molecules come from? The things around you. What if the things around you are smoke damaged, moldy, or remnants of a hoarding situation? In essence, little pieces of those elements, impurities, are getting inside of you.