I am very susceptible to the common cold. I get it at least 2 - 3 times a year. Sometimes it goes away in a couple of days, sometimes it develops into a nasty throat/lung infection with an awful cough and I need to take inhalers. I have no asthma in general though.

I have this theory that if the mucous that comes up in the cough and through the nose is yellow/green, then it is an infection and merits a doctor visit. if it is clear, then it is just a cold and I should wait it out.

Is the idea wrong?

  • 4
    A cold is an infection itself, so when you say "infection" do you mean bacterial infection? Or do you mean a lung infection in general, which can be viral or bacterial, such as in viral pneumonia?
    – Carey Gregory
    Commented Jul 8, 2015 at 0:03
  • 1
    I mean bacterial, that will require antibiotics
    – Victor
    Commented Jul 8, 2015 at 0:45
  • 1
    Many have this theory (myself included) - but I have no evidence to back it up (if I wind some, I'll post an answer). The only 100% certain way to tell if you have bacteria (and which) is to do microbiological tests of the sputum or of a swab, which of course implies a visit to the doctor's. If you don't get a better answer - anything that makes you really suffer, or last longer than a few days deserves physician's attention. If it's too difficult for you to go there (the office is far away or it would cause you to loose days from work) is there an option to consult with your doctor by phone?
    – Lucky
    Commented Jul 9, 2015 at 12:41

1 Answer 1


As has been pointed out in the comments, a common cold is already a (viral) infection. By far the largest part of upper airway infections are viral and the body is very capable of clearing them up.

It is a common misconception that that the colour of the mucus gives information about whether it is viral or bacterial. This study shows that the sensitivity of yellowish or greenish sputum used as a test for a bacterial infection was 0.79 (95% CI 0.63–0.94); the specificity was 0.46 (95% CI 0.038–0.53), which is very low.

A visit to your doctor for a cold is almost never necessary. Even in the case that there is a bacterial infection, your body can almost always get rid of it itself. This Cochrane review concludes that in acute, uncomplicated rhinosinusitis (which is, essentially, what we call "a cold") there is no place for antibiotics. It may cause the cold to be over faster than it would be without antibiotics, but without the antibiotics there is a very very low rate of complications. Antibiotics cause adverse events and resistance of bacteria, so they should not be used without reason.
As there is no reason for antibiotics, a visit to your doctor will also not be useful.

A subsequent upper airway infection with coughing is often caused by something called post-nasal drip (essentially mucus from the nose dripping into the throat), which sucks but doesn't warrent a visit to the doctor. Signs of a possible pneumonia are: fever for >3 days or recurrent fever after a few fever-free days, dyspnea or wheezing (this is based on the Dutch guidelines so I don't have an English source for this). In this case, I would definitely recommend going to your doctor. There is still a realistic chance that you're not going to need antibiotics, but that is a decision the doctor needs to make based on the specific circumstances and this cannot be assessed over the internet.

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