Common Cold

What the common cold is

A cold is an infection of the lining of the nose, sinuses and throat. Viruses enter through the eyes, nose or mouth, multiply in the nasal lining and trigger inflammation. That inflammation, rather than the virus directly, causes most symptoms: swelling (blockage), extra mucus (runny nose) and irritation (sneezing and sore throat). The medical term for the runny, inflamed nose is coryza, and doctors often call a cold an upper respiratory infection, or URI.

The main culprits are:

• Rhinoviruses: about 30 to 50% of colds. They grow best at the cooler temperature inside the nose.
• Seasonal coronaviruses (not the one that causes COVID-19)
• Adenoviruses, parainfluenza viruses, RSV and enteroviruses

Because there are so many viruses, and immunity to one does not protect against the others, you can catch colds again and again.

Common cold symptoms day by day

Symptoms start 1 to 3 days after exposure and build gradually:

Other common symptoms:

• nasal congestion and reduced smell and taste
• a mild headache or sinus pressure
• watery eyes
• hoarse voice
• low-grade fever, more common in children than adults
• mild body aches

Green or yellow mucus is normal in a cold. It reflects immune cells in the mucus, not a bacterial infection.

Cold vs flu, COVID-19 and allergies

A home test is the only reliable way to tell COVID-19 apart. Flu is worth recognizing early because antiviral medicine works best within 48 hours in people at high risk.

How colds spread and how long you are contagious

Cold viruses spread through:

• droplets from coughs, sneezes and talking
• hands: touching an infected surface or hand, then your eyes or nose
• shared objects such as toys, phones and door handles, where rhinoviruses can survive for hours

You are contagious from about a day before symptoms start and most contagious in the first 2 to 3 days. Viruses can still be shed for up to 2 weeks, though at lower levels. Children can usually return to school or daycare when they have no fever and feel well enough to take part, even with a runny nose.

Cold weather does not cause colds directly. Colds are more common in fall and winter because people gather indoors, and some research suggests a cold nose has weaker local defenses.

Treatment and remedies that help

There is no cure. These measures ease symptoms:

Home care

• Rest and fluids: warm drinks, soup and water loosen mucus and soothe the throat.
• Saline nasal spray or rinse: safe at every age. Use saline drops and gentle suction for babies.
• Honey: a teaspoon in warm water or tea eases cough in adults and children over 1 year. Never give honey to babies under 12 months because of the risk of botulism.
• Humidifier: cool-mist humidifiers are safest for children.
• Salt-water gargle and lozenges for sore throat (no lozenges for young children, who may choke).
• Raise your head at night to reduce post-nasal drip.

Over-the-counter medicines

• Acetaminophen (paracetamol) or ibuprofen for fever, aches and sore throat. Follow the label dose. Do not give aspirin to children or teenagers because of the risk of Reye's syndrome.
• Decongestant nasal sprays (oxymetazoline): no more than 3 days to avoid rebound congestion.
• Oral decongestants (pseudoephedrine): may help adults but can raise blood pressure and heart rate. Avoid them if you have high blood pressure, heart disease, glaucoma or an enlarged prostate.
• Antihistamines: older, sedating types can dry a runny nose slightly. Non-drowsy types do little for colds.
• Cough and cold medicines are not recommended for children under 4 in the US (and are generally avoided under 6). Check with a pharmacist for older children.

What does not work

• Antibiotics: they do not affect viruses and cause side effects and resistance.
• Vitamin C: taking it after a cold starts does not help. Regular daily use may shorten colds slightly.
• Zinc and echinacea: evidence is mixed. Zinc nasal sprays have caused permanent loss of smell and should be avoided.

Complications

Most colds clear without problems, but a cold can lead to:

• Acute sinusitis: symptoms over 10 days, facial pain, or a second worsening.
• Middle ear infection (otitis media): common in young children. Look for ear pain, fever and irritability.
• Asthma and COPD flare-ups: colds are the most common trigger of asthma attacks.
• Acute bronchitis and pneumonia: more likely in older adults, smokers and people with lung or heart disease. Watch for fever, breathlessness and chest pain.
• Croup and bronchiolitis in babies and young children, often from RSV or parainfluenza.

Preventing colds

• Wash hands with soap for 20 seconds, or use alcohol hand sanitizer.
• Avoid touching your eyes, nose and mouth.
• Stay home when sick, and cough or sneeze into a tissue or your elbow.
• Clean shared surfaces and toys during cold season.
• Sleep 7 or more hours. People who sleep less are more likely to catch a cold after exposure.
• Get flu and COVID-19 vaccines. There is no vaccine for the common cold, but these prevent illnesses that look like one.

Frequently asked questions

How long does a common cold last?

Most colds last 7 to 10 days. Symptoms peak around days 2 to 4, then slowly improve. A dry cough can linger for 2 to 3 weeks. If symptoms last more than 10 days without improvement, or get better and then worse, see a doctor to check for sinusitis or another complication.

Is a cold contagious?

Yes. You can spread it from about a day before symptoms start, and you are most contagious in the first 2 to 3 days. Smaller amounts of virus can be shed for up to 2 weeks. Hand washing and covering coughs reduce spread.

What is the difference between a cold and the flu?

A cold builds gradually and stays mostly in the nose and throat, with little or no fever. Flu starts suddenly with high fever, chills, severe aches and exhaustion, and is more likely to cause serious complications such as pneumonia. A flu test can confirm it.

What are URI symptoms?

URI stands for upper respiratory infection, the medical term for a cold or similar infection of the nose, sinuses and throat. Typical URI symptoms are runny or stuffy nose, sneezing, sore throat, cough, mild headache and sometimes a low fever.

Should I take antibiotics for a cold?

No. Colds are caused by viruses, and antibiotics only work against bacteria. They will not shorten your cold and can cause side effects such as diarrhea and allergic reactions. A doctor may prescribe them only if a bacterial complication like strep throat or sinusitis is confirmed.

Does green mucus mean a cold has become an infection?

No. Mucus often turns thick, yellow or green partway through a normal cold as white blood cells collect in it. What suggests a bacterial complication is symptoms lasting over 10 days, a high fever, severe facial pain, or getting worse after starting to improve.