How Long Is a Cold or Flu Contagious?

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Are you too sick to work?

Are You Too Sick to Work?

First and foremost, consider whether you are putting yourself or others at risk if you go to work. You're putting others at risk if you or your children have a contagious illness (more on that later). You're putting yourself at risk if the symptoms of your condition, or the side effects of medication, could cause you to have an accident on the job, injure others, or produce devastating mistakes in your work product. Putting anyone in harm's way is a clear reason to stay home.

How long is a cold or flu contagious?

Both colds and the flu are contagious and are caused by viruses. However, the viruses that cause colds (for example, rhinoviruses) are not the same as those that cause the flu (influenza viruses). Although the typical incubation period for influenza is about one to four days, some adults can be contagious from about one day before onset of symptoms for up to two weeks. Other people who develop complications, such as pneumonia, may extend the contagious period for a week or two. For colds, most individuals become contagious about a day before cold symptoms develop and remain contagious for about five to seven days. Some children may pass the flu viruses for longer than seven days (occasionally for two weeks).

Colds are considered upper respiratory infections. The flu may also cause lower respiratory infections.

How will I know if I have a cold or the flu?

For both the cold in the flu, early symptoms may be similar. Symptoms and signs include a cough, runny nose, and feeling tired. If you know you have had contact with someone with a cold or the flu in the past few days, you should suspect you may have become infected. However, flu symptoms generally are more intense than cold symptoms. People with flu can develop fever, body aches, chills, and headaches, and some develop nausea and vomiting. Cold symptoms are much milder and usually do not require medical care. However, if you suspect you have the flu, you should seek medical care. The flu often can be diagnosed with rapid tests available to most physicians.

How do cold and flu viruses spread?

A common cold and the flu are easily spread from person to person, the flu most often by droplets produced by coughing and sneezing. Cold viruses in droplets are spread mainly hand to hand. These droplets contain the infectious viruses. Occasionally, these droplets land on various surfaces and, depending on the survivability of the virus type, can be transferred when an uninfected individual touches the contaminated surface and subsequently touches his/her mouth or nose.

How will I know if I am cured of the flu or a cold?

In most instances, individuals with a cold will resolve their symptoms without medical intervention in about one week, although sometimes the cough may last longer. However, at this point in time, the cough is not spreading contagious virus. When cold symptoms and signs resolve, a person is cured of a cold. The flu is similar except that the symptoms are more severe and, in some individuals, medical intervention may be required (for example, antiviral medications). However, depending upon the influenza strain the severity of infection, some individuals may require hospitalization. The cure for these individuals occurs when symptoms resolve and the patient is discharged the hospital.

The stomach flu is not caused by cold or by flu viruses. The term stomach flu is a nonspecific term that describes symptoms of nausea, vomiting, and diarrhea. Although these symptoms may occur with the flu, the flu is a respiratory infection. In most individuals with only stomach flu, the causes are usually non-flu type viruses. Similarly, cold sores are not actually caused by cold viruses but by herpesviruses.

Medically Reviewed by a Doctor on 1/18/2017

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