A 2015 study concerning the association of SBS and indoor air pollutants in office buildings in Iran found that, as carbon dioxide levels increase in a building, symptoms like nausea, headaches, nasal irritation, dyspnea, and throat dryness have also been shown to increase. Certain work conditions have been found to be correlated with specific symptoms. For example, higher light intensity was significantly related to skin dryness, eye pain, and malaise. Higher temperature has also been found to correlate with symptoms such as sneezing, skin redness, itchy eyes and headache, while lower relative humidity has been associated with sneezing, skin redness, and pain of the eyes.