The Immune System’s Role
The human body's immune system is extremely complex, and is not yet fully understood by scientists. The main function of the immune system is to defend the body against foreign pathogens, such as viruses, bacteria, and germs that can attack the body, causing infection and illness. According to the National Institutes of Health, the immune system’s job is to keep harmful infiltrators out or, when they enter the body, to seek out and destroy them.1
The Progression of a Cold Virus
The common cold begins as a viral infection of the upper respiratory tract. The infection almost always runs the same course; however, colds can vary in severity depending on the virus and a person’s immune system. Here are more facts about the progression of a cold:
- People are most contagious during the first two to three days of a cold.2
- Cold symptoms generally increase in severity, and peak in about two to three days.3
- The first symptoms of a cold may include runny nose, itchy or scratchy throat, sore throat, and sneezing.3 Fever does not usually occur in adults and older children, but is common in younger children.2,4 Depending on the virus, other symptoms may include a cough, headache, nasal discharge, and nasal congestion.3
- Within a few days, the fluid from a runny nose may change color from clear to yellow to green, and a cough may become productive.3
- The typical cold can last up to 10 days. Some symptoms, such as a cough, can linger up to three weeks.
- After recovering from a cold, the immune system builds up antibodies to defend itself from catching that particular cold virus again.1,5 However, because there are numerous strains of cold viruses, the immune system is still susceptible to other strains.5
If you have a cold, contact your doctor if breathing becomes difficult or if symptoms worsen or do not improve after seven to 10 days.2
Learn more about how your body fights off the cold and flu.
Heikkinen, T., Järvinen, A. The common cold, The Lancet. 361:51-58.16. 4 Jan 2003.
Turner, R.B. The common cold. In: Mandell, G.L., Bennett, J.E., Dolin, R., eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia PA: Elsevier Churchill Livingstone; 2009: Chap 53.