Allergy vs Cold Allergies and the common cold are both conditions that can cause similar symptoms, but they have different underlying causes. Here are the key differences between allergies and a cold: 1. Cause: - Allergies: Allergic reactions occur when the immune system reacts to substances (allergens) that are typically harmless. Common allergens include pollen, pet dander, certain foods, and dust mites. - Cold:Colds are caused by viruses, most commonly the rhinovirus. Other viruses, such as t