A runny nose and sneezing are symptoms common to a cold or an allergic reaction, so it may be easy to mistake one for the other, but colds and allergies are completely different conditions. A cold is a viral infection, usually caused by one of the many rhinoviruses that infect the nasal passages. Colds are contagious, and may be caught from contact with an infected person, or breathing air containing viral particles. An allergy is an immune reaction to a harmless substance, such as pollen or mold. Allergies may affect the nose, throat and eyes of a person sensitive to the offending substance. An allergy is not contagious, but people with family history of allergy are more likely to get allergies.
Onset
Colds symptoms start one to three days after an infection begins, and the virus is most contagious during the first days after symptoms develop. Initial symptoms of a cold include scratchy throat, sore throat or discomfort in the nose, the Merck Manual notes. Symptoms of an allergy begin immediately after exposure to the offending substance, and may be mild or severe all at once. Colds are common during the colder months, while allergies, especially seasonal, usually flare up anytime from spring to fall.
Nasal Symptoms
Runny nose, sneezing and a stuffy nose are symptoms common to colds and allergies. But mucus from a cold virus will start out as watery and clear, and becomes yellow-green and opaque as the illness develops. Itchy eyes, itchy nose, and sneezing are uncommon in a cold. The mucus from an allergy will look consistently clear and watery, unless complications from a sinus infection develop, then the mucus becomes opaque and yellow-green as well and the lining of the nose becomes swollen and bluish red. Itchy eyes, nose and throat and sneezing are common symptoms in an allergy.
Fever and Aches
A low-grade fever may occur at the beginning of a cold, and young children may run a fever between 100 to 102 degrees F, according to the University of Maryland Medical Center. A person with colds may also experience slight body aches or mild headaches. Fever is never a symptom of an allergy, although fatigue may occur with either a cold or an allergy.
Coughing
Coughing and a sore throat usually accompany cold symptoms, but the cough comes from the throat. Coughing sometimes accompanies an allergy, and if it does, there may be whistling or wheezing sounds coming from deep in the lungs. Breathing difficulty due to constricted airways causes coughing and wheezing in an allergy.
Duration
Cold symptoms usually lasts from four to 10 days, and coughing may continue beyond that. The symptoms worsen as the cold progresses and then gradually improve. Symptoms of an allergy immediately begin after exposure and last as long as the exposure continues. In the spring or fall, allergies may last through the entire season.
