Air purifiers and humidifiers serve different purposes when addressing allergies. While air purifiers help remove allergens, dust, and other particles from the air, humidifiers provide moisture into the air while eradicating some of the larger particles from the environment. Carver cautions against using humidifiers all the time, though, because the added moisture could actually make one’s allergies worse. “Too much moisture can lead to mold growth and more dust mites, both of which trigger asthma and allergy symptoms,” Carver says, adding that mold and dust mites thrive in environments with humidity above 50 percent. “Mold spores can get in your nose and cause allergy symptoms. Spores can also get in your lungs and trigger asthma,” she says. Humidifiers are only recommended to keep humidity between 30 to 50 percent. Otherwise, Carver says some people might need a dehumidifier if they live in a humid environment, because “if the air is too humid, air purifiers won’t work properly.”