How Long Is a Cold or Flu Contagious?

Common cold viruses typically become contagious about two to four days after symptoms begin, and people usually remain contagious with a cold for about a week. People with the flu are most contagious in the first three to four days after their illness begins. You may be contagious before you even feel sick.

The common cold is a type of mild upper respiratory viral infection. Common colds are the most frequent acute illness in the U.S. and the industrialized world and occur more frequently in winter and spring, but they can occur any time of year. 

The flu (influenza) is a respiratory illness caused by influenza viruses. It can cause mild to severe illness that can result in hospitalization or death. There are two main types of flu (influenza) virus: types A and B that are responsible for seasonal flu epidemics each year.

The "flu" (influenza) and the common cold also have symptoms similar to COVID-19, however, COVID-19 can cause more severe symptoms and complications.

Symptoms of a cold usually peak within 2 to 3 days of infection and may include:

• Sore throat
• Runny nose
• Stuffy nose
• Coughing
• Sneezing
• Headaches
• Body aches
• Post-nasal drip
• Watery eyes
• Fever (most people with colds do not have fever)

A cold usually lasts about 7-10 days, but some symptoms, especially runny and stuffy nose and cough, can last for up 2 weeks.

Symptoms of flu (influenza) usually come on suddenly and may include:

• Fever (not everyone with the flu has a fever) 
• Chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue/tiredness
• Vomiting and diarrhea (more common in children)

More than 200 known viruses can cause the common cold, but rhinoviruses are the most common type. Adenoviruses and enteroviruses also cause the common cold.

Factors that may increase the risk for catching a cold include:

• Close contact with someone who has a cold
• Season: certain viruses are more common during certain times of year
• Age: infants and young children have more colds each year than adults

The flu (influenza) is a caused by influenza viruses transmitted from person-to-person through respiratory droplets thrust into the air when an infected person coughs or sneezes. Less commonly, the flu is transmitted when a person touches a surface or object that has the virus on it, and then touches their mouth, nose, or eyes.

Both the common cold and the flu (influenza) are contagious and the viruses that cause these illnesses are spread from person to person through respiratory droplets released into the air when an infected person coughs or sneezes. 

They can also be transmitted by hand-to-hand contact or by touching surfaces contaminated with the virus and then touching your mouth, nose, or eyes.

Common cold viruses typically become contagious about 2 to 4 days after symptoms begin, and people usually remain contagious with a cold for about a week, but they may be contagious until all symptoms disappear, which can take several weeks. 

People with flu are most contagious in the first three to four days after their illness begins. Symptoms of the flu usually start within 1 to 4 days after exposure to the virus, and you may be contagious before you even feel sick.

The Centers for Disease Control (CDC) recommends staying home from work or school for at least 24 hours after fever has gone away on its own, without the use of fever-reducing medications. The flu is generally considered contagious for at least a week after symptoms start.

The common cold and influenza (the flu) are diagnosed based upon the patient’s reported symptoms and a physical examination. 

Testing of any kind is not usually needed to diagnose the common cold. 

Tests may be used to rule out other infections that cause similar symptoms to the common cold:

• Nasal swab testing for coronavirus disease (COVID-19)
• Rapid influenza diagnostic tests (RIDTs) or rapid molecular assays for the flu (influenza)
• Chest X-rays for lower respiratory tract infection 

Influenza (the flu) is usually diagnosed with: 

• Rapid influenza diagnostic tests (RIDTs) 
  • Provides results in about 15 minutes
  • Less accurate than other flu tests called 
• Rapid molecular assays 
  • Detects genetic material of the virus and provide results in about 15-20 minutes
• Other specialized flu tests may be used in hospitals or state public health laboratories
  • Specialized tests use a long swab to swipe the inside of the nose or the back of the throat, which is sent to a lab for testing
  • Results may take several hours

There is no cure for the common cold. Antibiotics do not help treat colds caused by viruses. 

Antiviral medications may be used to treat the flu (influenza) and they work best when taken within 48 hours of the onset of flu symptoms to help reduce the severity and duration of the illness. 

• Oseltamivir phosphate (Tamiflu)
• Zanamivir (Relenza)
• Peramivir (Rapivab) 
• Baloxavir marboxil (Xofluza)

Home remedies to help relieve symptoms of both the common cold and the flu include: 

• Rest
• Drink plenty of fluids
• Use a clean humidifier or cool mist vaporizer
• Use saline nasal spray or drops
• Breathe in steam from a bowl of hot water or shower
• Suck on lozenges (do not give lozenges to young children as they can be a choking hazard)
• Over-the-counter (OTC) medicines for relief of symptoms 
  • Pain relievers and fever reducers such as aspirin, acetaminophen (Tylenol), and ibuprofen (Advil, Motrin)
    • Don’t give aspirin to children because it can cause Reye’s syndrome, a rare but serious illness 
  • Cough and cold medicines