High levels of indoor pollutants can cause immediate symptoms after one or more exposures. The symptoms may look like those of a cold or virus, including irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. These effects are usually short-term and reverse quickly once the person leaves the building or the pollutant is identified and eliminated. Short-term exposures can also trigger asthma episodes and lead to other serious allergic responses, including hypersensitivity pneumonitis and humidifier fever, both of which may first appear as flu-like symptoms.
For many pollutants, the exposure level at which symptoms first appear is highly variable. For example, mold, pollen, insect fragments, insect fecals, and animal protein (dander, etc.), elicit a range of allergic reactions in some, while others are unaffected.