While asbestos can’t be directly absorbed through the skin—the fibers are too big—skin contact can still produce symptoms. Contact dermatitis can flare up in sensitive individuals but in most cases, the danger from asbestos comes from inhaling the fibers, or dust, that is produced when asbestos is disturbed. If you touch asbestos by accident, immediately wash yourself and your clothes.

Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

Some pros may recommend covering a popcorn ceiling that tests positive for asbestos with beadboard ceiling planks or drywall. The cost to install a beadboard ceiling averages more than $5,000, but you likely will pay more than the average for the installer to deal with the asbestos safely. Installing a beadboard ceiling or new drywall will disturb the asbestos and release some microscopic fibers, so the installer will need to take precautions. 

Asbestos was most commonly produced and integrated into building products from the 1920s to the late 1980s. In reality, asbestos use should have ceased much sooner because asbestos was linked to cancer in studies produced as early as the 1950s. You can even extend that number past the 1980s due to stockpiled materials and because some countries treat asbestos use differently. It may also be found more in commercial applications than residential.