Unless you have a profession like pro surfer, you probably spend the majority of your days indoors. And the air in your home or office can be filled with harmful toxins and pollutants like formaldehyde and ammonia. These can cause a range of health issues, from eye irritation to respiratory problems. NASA—yes, that NASA—conducted a study that found houseplants can seriously improve indoor air quality by filtering out harmful toxins. Here, the 18 best plants to give your space a wellness boost.