Basic Symptoms
Colds and allergies are so difficult to discern, because they both begin with nearly the same symptoms: cough, sneezing, watery eyes, possible headache and runny or stuffy nose. Colds typically last for one to two weeks, whereas allergy symptoms last as long as the offending allergen is present (or sometimes a bit longer). This can be days, weeks (as with hay fever symptoms) or even months.
Identifying Distinctions
A few key symptoms can correctly identify a cold or allergy. A clear runny nose that changes to thick or colored discharge after a few days indicates an infection, often viral but possibly bacterial in origin. Similarly, a fever is never associated with a pure allergic reaction but may occur during a cold's progression. In addition, aches and body fatigue almost never occur with allergy but may occur with a cold. Although eyes may be watery with either cold or allergy as a result of nasal symptoms, only allergy causes eyes to itch as a histamine-induced reaction to an allergen. Finally, progression of cough from a dry or hacking type to a more productive or wet cough may indicate a cold or more extended infection rather than an allergy.