Flu, cold or allergy: how to tell them apart

Every winter brings the same confusion. You are sneezing, your throat is scratchy, you feel drained — but is it a common cold, the flu, or an allergy flaring up? The distinction is not academic: it changes what you should do, how long the symptoms will last, and whether you need to see a doctor.

Three different mechanisms

A cold is caused by mild respiratory viruses, mainly rhinoviruses. Flu is caused by influenza viruses, which are considerably more aggressive. A respiratory allergy is not an infection at all: it is an excessive immune reaction to a harmless substance — pollen, dust mites, animal dander, mould.

The comparison table

Sign	Cold	Flu	Allergy
Onset	Gradual (1–3 days)	Abrupt (within hours)	Immediate after exposure
Fever	Rare or mild	High, 38.5–40 °C	Never
Body aches	Mild	Intense, widespread	Absent
Fatigue	Moderate	Marked exhaustion	Variable, from poor sleep
Sneezing	Frequent	Possible	In repeated bursts
Itching (eyes, nose)	No	No	Highly characteristic
Duration	7–10 days	1–2 weeks	As long as exposure lasts

The most useful shortcut: high fever and intense body aches point to flu, while itchy eyes and bursts of sneezing point to allergy. A cold sits in between — unpleasant, never abrupt.

What to do in each case

Cold

No treatment shortens a cold. Rest, drink plenty of fluids, rinse your nose with saline. Antibiotics are useless: a cold is viral. If symptoms last beyond 10 days or worsen after improving, see a doctor — a bacterial superinfection is possible.

Flu

Strict rest, hydration, paracetamol for fever and aches. Isolate yourself for the first few days: flu is highly contagious. Annual vaccination remains the best protection, and is particularly recommended for people over 65, pregnant women, people with chronic conditions and healthcare workers.

Allergy

Identify and limit exposure to the allergen. Antihistamines provide effective relief. If symptoms return at the same time every year or disrupt your sleep, a consultation can lead to allergy testing and a longer-term treatment plan.

Limiting contagion around you

Colds and flu spread through droplets released when speaking, coughing or sneezing, and through hands touching the face after contact with a contaminated surface. A few habits markedly reduce the risk:

• wash your hands with soap several times a day, especially before meals;
• cough and sneeze into your elbow, never into your hand;
• use single-use tissues and discard them immediately;
• air rooms for around ten minutes twice a day;
• wear a mask around vulnerable people — infants, pregnant women, the elderly.

For allergy sufferers the logic is reversed: the aim is not to protect others but to reduce your own exposure. Close windows during peak pollen hours, rinse your hair in the evening, wash bedding at 60 °C against dust mites, and avoid drying laundry outdoors in spring.

When to see a doctor

• Fever above 39 °C lasting more than 3 days.
• Difficulty breathing, shortness of breath, chest pain.
• Worsening after a period of improvement.
• Symptoms in an infant, a pregnant woman, an elderly or immunocompromised person.
• A cough lasting more than 3 weeks.

In most cases, a remote medical opinion is enough to settle the question. If you are unsure what to do next, the symptom questionnaire points you in the right direction in a few clicks. You can also see a general practitioner by video the same day, with no waiting room — which also avoids exposing other patients.