Respiratory allergens and pollutants can trigger a wide range of symptoms, including allergic rhinitis, sinusitis, headaches, fatigue, nausea, depression, dermatitis, rash, sore throat, nasal congestion, and itchy or watery eyes. The estimated 50 to 60 million Americans and more than one billion people worldwide afflicted with allergies, asthma, or other resiratory problems are most severely affected. People with weakened immune systems, can be especially susceptible to more severe complications, such as bronchial infections or pneumonia. While medical science has made great strides in developing medications to treat reactions to allergies, health professionals generally recommend reducing or eliminating exposure over merely treating the symptoms.