Colds and allergies have different causes. Colds are caused by viruses. Allergies occur due to exposure to allergens, such as pollen, dust, or mold. Colds are contagious, whereas allergies are not.2
Other differences between colds and allergies are: how fast symptoms can appear, how long they last, and the time of year in which they occur. An important difference is that colds generally don’t last longer than 10 days. If you still have symptoms after 10 days, it may be allergies.2 Talk to your doctor.