How do i know if i have virus or allergy?

Difficult: It is often difficult to tell which of these is bothering you, as they can both caues similar symptoms (runny nose, congestion, sore throat, fatigue, sinus pressure, etc). Clinicians can sometimes tell them apart with blood work or appearance of the nasal mucosa (skin inside the nose), but often it doesn't matter because they are usually treated the same. Allergies, however, do not cause fevers.

Fever?: Viruses affect the whole body with muscle pains, sore throat, cough, increase phlegm/sputum production, fever. Allergies cause itchiness, watery and burning eyes, sneezing but less likely muscle pains cough or fever. Both cause nasal discharge ( clear if allergic, green or yellowish with viruses or bacteria) and nasal congestion with obstruction, possible itchy throat.