When are colds contagious?

Dear Alice,

When is a person with a cold contagious? A couple of friends, who are put off when I keep my distance from their sneezing and coughing, insist one is only contagious a week or so before symptoms appear. In the back of my memory is the idea that one remains contagious until a few days *after* primary symptoms disappear. I'm not usually so concerned about this, but I'm coping with a couple of other annoying health problems and want to try to avoid adding a cold or flu, to boot. I do the usual things news shows recommend — eat well, wash hands frequently. But when should one avoid others who have colds, or when should one stay isolated at home when one has a cold (or flu)?

Healthy and wanting to stay that way

Dear Healthy and wanting to stay that way,

The common cold, also known as an upper respiratory infection (URI), can be caused by any of more than 200 viruses. These viruses attack and multiply in the cells that line the nose and throat. Colds are often spread through touch. If you shake, contact, or hold the hand of an infected person (who may not have apparent symptoms), and then touch your eyes or nose, you are likely to infect yourself with the virus. In addition, you can "catch" a cold if you touch your eyes or nose after touching a hard, nonporous surface, such as a telephone or doorknob, shortly after an infected person touched it. The best way to prevent a cold's transmission is to wash your hands frequently with soap and warm water (as you mentioned).

Viruses can also be transmitted in the small airborne particles produced by a cough or a sneeze, but this requires very close contact. Whether or not you come down with a cold once you've been exposed to the virus depends on a variety of factors, including your age, genetics, type and amount of exposure, whether or not you smoke, and whether you've developed antibodies to that particular virus. Studies show that, if you contract a cold, you can transmit it to others one or two days before your symptoms appear, and up to four or five days after first being exposed to the virus. According to the National Institutes of Health (NIH), colds are most contagious two to four days after original exposure (whether or not symptoms have developed), when there is plenty of the virus present in nasal secretions.

Some basic information on how colds "work": cold-causing viruses fall into three families — rhinoviruses, coronaviruses, and adenoviruses. Like all viruses, those that cause colds trick cells in the body into ingesting them and then take over the cells' reproductive machinery to make new viruses. When an infected cell dies, new virus particles are released and go on to infect other cells. Some of the symptoms of a cold are caused by the actions of the virus. For example, destruction of cells lining the respiratory tract or throat can cause sore throat, cough, and runny nose. Other symptoms are caused by the body's immune reaction to the virus. When the body recognizes the viruses as foreign, immune cells release interferons and leukotrienes, which help mobilize the body's defenses, but also cause fever, aches, and fatigue.

Adults average two to five colds a year. If you do catch a cold, the general advice is to get plenty of rest, drink lots of fluids, avoid overmedicating yourself, and stay away from cigarette smoke. Some people swear by vitamin C. Additionally, here's some advice for specific symptoms:

  • Headache, body aches, and fever: Take acetaminophen, ibuprofen, or aspirin.  
  • Thirst and dehydration: Drink a glass of water, juice, broth, or tea every hour or two while you are awake. Avoid caffeine and alcohol, which can increase your congestion and dehydration.
  • Sore throat: Take aspirin or aspirin substitutes. Also, gargle with 1/4 teaspoon of salt or baking soda in a glass of warm water. Lozenges, hard candy, and throat sprays help soothe your throat.
  • Cough: Add moisture to the air by using a humidifier or placing a pan of water on your radiator. Cough medicines containing the suppressant dextromethorphan (DM) or Throat Coat tea (from health food stores) may help to ease the cough.
  • Congestion: Decongestants, such as pseudoephedrine, relieve congestion. Antihistamines, such as chlorpheniramine, can alleviate runny noses. There are also combinations of decongestants and antihistamines that do both. Breathing steam for ten minutes several times a day reduces congestion. Fill a bowl or sink with steaming tap water, and bend your head over the bowl, placing a large towel over your head to trap the steam. Some people prefer to breathe in the steam created while showering.

It is only necessary to see a health care provider if you have any of the following symptoms:

  • Cold lasting more than ten days
  • Dark green, very thick, or bloody phlegm
  • A fever of higher than 101.5 ° F for more than three days
  • A rash
  • Chest pain, shortness of breath, or wheezing
  • Ear pain, loss of hearing, or severe facial pain
  • Severe dizziness

If any of these symptoms are present, see a health care provider as soon as possible.

The old, tried and true remedies for a cold, as we all know, are to stay in bed and get plenty of rest, drink lots of fluids, and have some chicken soup and a little TLC (tender loving care).

Last updated Jul 30, 2015
Originally published Feb 10, 1995

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