Nasal congestion is commonly caused by allergic rhinitis, or hay fever. This occurs when pollen, dust, mold spores, or other allergens are inhaled and irritate the nasal passage. Other causes of nasal congestion include the common cold or flu, a deviated septum, sinusitis or sinus infections, reaction to certain medications. Additionally, nasal congestion occurs in many women during pregnancy. In many individuals, nasal congestion is caused by food allergies. Those who are lactose intolerant often find themselves suffering from a stuffy nose. Your doctor can conduct allergy tests to identify your specific type of food allergy and recommend a new diet. Reducing the amount of dairy in your diet in addition to carbohydrates and sugar can improve the quality of your diet and reduce nasal congestion.