Dust is a real problem with fiber optics. It's granular in nature and resists compression. It often is opaque and completely blocks the optical signal. Getting rid of the dust is a top priority.
There are two basic sources of dust-based contamination: 'wear debris' and 'environmental.
The most common source is wear debris caused by the friction of inserting a connector into the adapter. Connectors like the SC and MPO have sliding housings that are held in place by latches in the adapter. Other connector systems like the ST, FC, and many of the hardened connector systems have metal housings that are threaded and use orientation keys. All of these connectors wear through repeated matings and generate particles of dust and debris. Other sources of wear debris are the protective end caps. Removing the end caps from a connector which was perfectly clean during the last inspection at factory will cause the end-face to become contaminated when the end cap is removed by the installer.
The other common contributors for dust-based contamination is our environment. The common sources of dust in the air that contribute to dust-based contamination include: skills cells, hair, clothing lint, debris from foam-based swabs, poor quality paper wipes, zinc whiskers from electroplated surfaces, cardboard packaging, plant pollen, molds, airborne dirt and sand, abraded concrete, carpet dust, pollution from electricity generation, and vehicle emissions.
Either type of dust can be 'locked' on to an end-face by static charges. Use the Sticklers cleaning fluid to dissipate the static charge and improve the cleaning results. Remember: always clean your connectors, both sides, every time you are mating them.