Allergies vs a cold: how to tell?

The itch is the first tell: allergies itch, eyes, nose, throat, sometimes ears, while colds almost never itch. Then the timeline: cold symptoms build over a day or two, peak, and resolve in 7 to 10 days; allergy symptoms start abruptly on exposure and last as long as the allergen is around, which is why "a cold" that has lasted 3 weeks in April is usually pollen. The symptom split, per MedlinePlus's descriptions of both: allergies bring sneezing fits, clear and watery nasal drainage, itchy watery eyes, and no fever and no body aches; colds bring a sore throat first, thicker mucus that may turn yellow or green (normal for viruses, not a bacteria sign), possible low fever, body aches, and sometimes a cough that lingers into week two. The calendar and context do the rest: symptoms every spring or fall, around pets, or after yard work point to allergies; symptoms after a sick kid or a flight point to a cold. The self-experiment that settles it: a non-drowsy antihistamine (cetirizine, loratadine) noticeably improving things within hours points to allergies, since antihistamines do nothing for viruses. Treatment follows the answer: colds get rest, fluids, honey for the cough, and acetaminophen for aches; allergies get antihistamines, daily nasal steroid sprays during the season, saline rinses, and trigger reduction (showering off pollen, closed windows on high-count days). Both can muddy each other: allergies inflame the nose in ways that invite sinus infections and make colds more likely. The see-a-doctor patterns: "colds" that never fully leave (likely allergies worth testing), sinus symptoms past 10 days either way, wheezing with either (asthma territory), or allergy symptoms that over-the-counter treatment cannot control, which is when allergy shots enter the conversation.