Several studies show a link between photocopiers and sore throats, skin irritation, asthma, and other health problems. That's because copy machines emit several toxic gasses, such as nitrogen dioxide and ozone.

Certain laser printers pose health risks, too. They emit tiny particles small enough to enter the human bloodstream by burrowing deep within our lungs. That can hurt your lungs and heart. 

Scientific studies have found air purifiers both ineffective and dangerous. They don't remove carbon monoxide as many manufacturers claim, and they don't remove dust or pollen.

Sadly they can actually make indoor air quality worse by reacting to other contaminants to create new, harmful byproducts.

When a new carpet is installed, there's a very good chance it will release chemicals from its vinyl backing and the glue used to hold the carpet to the floor.

These chemicals can be released for as long as five years after a new carpet is installed, but the majority of the off-gassing takes place in the first few months. 

Home products with formaldehyde include wood furniture such as cabinets and items using particleboard or plywood, as well as laminate flooring. These products release most of their formaldehyde after two years.

When it is released into the air, formaldehyde can irritate your skin, eyes, nose, and throat, and may cause breathing problems.

What do you use to clean your home? Chances are you use multiple cleaners or sanitizers. When these substances interact in the air you breathe, they can form complex VOCs that have been linked to various health problems.
Non-stick pans are safe to buy however a toxic chemical can be released from overheating your cookware. 

Of course try not to let people smoke around you or in your car—whether or not the windows are open. 

Using wood or charcoal to heat your home may be a quaint way to stay warm, but it also adds harmful substances to the air you breathe.

The convenience of natural gas is countered by the noxious gases these appliances emit: carbon monoxide (CO), nitrogen dioxide (NO₂), and even a bit of formaldehyde.

One study found that CO and NO₂ levels are substantially higher in homes with gas ovens, especially in the winter when people are less likely to open their windows. 

Air fresheners have been found to contain phthalates, formaldehyde, and other harmful chemicals, and often those chemicals are not listed among the product's ingredients as they may be considered trade secrets. One study found phthalates in 86% of the air fresheners it tested.

Phthalates are used commercially to soften plastics, make nail polish more adherent, and can be found in perfumes as well.

Pets who shed such as dogs and cats leave skin flakes known as dander in the air. Dander is an allergen for many, and can cause wheezing, irritation or coughing fits. The length of a pet's hair is irrelevant, since it's the dander that causes irritation. 

The best remedy is to double down on housekeeping. Keep floors vacuumed and mopped. Have someone who is not allergic wash the walls down regularly too.