Colds are commonly caused by viruses and are therefore contagious. The virus enters your body through the mouth, eyes, or nose. It also is spread through droplets in the air when someone who has a cold coughs and sneezes. Spread can also occur by touch or contact with someone who is sick by sharing contaminated items, such as eating utensils, phones, hand towels.
Allergic rhinitis, unlike a common cold, is not caused by any virus. Therefore, it is not contagious. Allergies occur when a foreign object, such as dust, dander or pollens, enter the body and are mistakenly identified by the immune system as an invader. In response, the body releases histamines in the blood. These unleashed histamines can lead to symptoms similar to a common cold, and delicate mucus membranes in the nose and respiratory tract may swell, and your nose may become stuffed up or runny.