Regular duct cleanings are an easy way to keep air circulating through the home, though not as satisfying as punching a hole in every wall. Feel a calming breeze with this Groupon.

The Deal

• $89 for air-duct cleaning for up to 12 vents ($180 value)

Dust Mites: Invisible Flesh Eaters

Dust mites exist wherever humans do, eating our shed skin and making our eyes itchy. Read on for more about these tiny garbage disposals.

Dust mites are permanent houseguests, freeloading off of our dead skin cells and making themselves comfortable in our beds. Unlike a distant relative or a persistent vacuum salesman, they're hard to kick out since they're nearly impossible to see. Each mite measures about 1/80th of an inch, visible only under the lens of a microscope. Close up, they echo back to something prehistoric. Their eight legs are equipped with suckers and hooks, and their thick bodies seem to be covered in armored plates. In fact, fossil evidence suggests that mites have been on Earth for 400 million years, predating dinosaurs by more than 100 million years. And since that time, they've made themselves at home inside damp, dark spaces brimming with dead skin cells, their current favorite homes being carpets, duvets, and pillowcases. Humans make it easy for mites to find food, since we shed about 1.5 million skin flakes every hour.

Although our relationship with mites is partially symbiotic—they do dispose of our biological waste—mites also pose a health threat, especially to children. Their droppings can trigger asthmatic reactions in those with mite allergies, and their terrifying appearance can give any kid with a microscope a new reason to fear the boogeyman under the bed.