They may smell sweet, but when it comes to your health, synthetic fragrances stink. A 2007 study of six fragranced consumer products discovered that the cleansers emitted nearly a hundred different volatile organic compounds (VOCs), chemicals released as gas. These included acetaldehyde and 1,4-dioxane, which cause immediate eye, skin, and airway irritation. And weekly use of common glass cleaners, furniture sprays, and air fresheners has been linked to a 30 percent to 50 percent increased risk of adult asthma. Plug-in air fresheners, in particular, emit a constant cloud of VOCs called terpenes, a class of pine- or lemon-scented plant oils. While not themselves toxic, terpenes off-gas formaldehyde when mixed with ozone, resulting in watery eyes, wheezing, and inflamed airways. That said, current consumer laws don't require labels to list VOCs or fragrances — even if they cause respiratory problems.

How to avoid them: Avoid using ionizing air purifiers, which can produce indoor ozone, a molecule that is highly reactive when placed in contact with other substances — especially air fresheners that emit terpenes. Rather, neutralize odors with Boston ferns, bamboo palms, and spider plants, which also absorb toxins such as formaldehyde and benzene. Instead of sprays and aerosols, use essential oils diluted in water to reduce your exposure to airborne chemicals.