The common symptoms reflect that each condition affects your respiratory system, says the National Institutes of Health.
While both colds and flus can cause congestion, cough and sore throat, the flu has unique symptoms. The flu can cause high fever, headache, fatigue, and aches. These symptoms are less common in people with a cold.
Allergies can cause itchy, watery eyes, which aren't typical symptoms of a cold or flu. Usually, allergy symptoms last as long as you're exposed to the trigger. A cold or the flu rarely lasts more than two weeks.
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