How it happens: You inhale Legionella, pneumonia-inducing bacteria that thrive in water and are found in industrial air-conditioning units and water pipes. The result is Legionnaires’ disease, named after a 1976 American Legion convention where the bacteria killed 29 people.

The fix: Every 3 months, crank your hot-water heater above 140°F and run all the faucets on hot for 10 minutes. The heat kills off the bacteria.

How it happens: You replace your incandescent lightbulbs with more energy-efficient compact fluorescent lightbulbs (CFL). But when these eco-friendly beacons break, they release mercury gas, a neurotoxin that attacks the nervous system and can cause chronic kidney problems.

The fix: Hold the bulbs by the plastic base, not the glass, when inserting and unscrewing them. Put spent bulbs into the original boxes or in double plastic bags before recycling them.

How it happens: Those assembly-required bookshelves may be more trouble than they’re worth. Particleboard is glued together with the toxin formaldehyde, the vapors of which irritate the eyes and skin of some people, according to the Centers for Disease Control and Prevention.

The fix: Slap on a coat of varnish to trap the formaldehyde. You’ll stave off exposure and hide cheap shelves.

How it happens: Your home may be built on soil with dangerous levels of decayed uranium, called radon. “A home is like a vacuum cleaner over soil,” says Laquatra. Radon is the second leading cause of lung cancer. (Cigarettes are the first.)

The fix: Conduct a radon test every 2 years. If your home fails the test, hire a contractor to install a ventilation pipe that stretches from below the basement floor to above roof. It will siphon off the deadly radon particles - an easy fix for a dangerous problem.