Most of us have gotten cold symptoms at least once every winter. The symptoms that occur in a common cold or upper respiratory tract infection are predictable and often occur in a sequence. If you are aware of this timeline, you will be better able to know what is coming and how long it will last. Many people with a common cold do not need to see a doctor. If you start experiencing more severe symptoms such as fever lasting for more than a day or two, you may need to see a medical provider.
Most colds are not due to the “flu”. Rhinoviruses cause 30-50% of cases and coronaviruses are the second most common culprit, accounting for 10-15% of colds. Influenza viruses only cause 5-15% of upper respiratory infections.
The timeline of a typical cold is as follows:
You breath in the virus through contaminated air or you touch a contaminated surface. The virus is transferred from your hands to your mouth or nose. The virus then infects your upper airway.
Your immune system reacts by activating macrophages (specialized disease-fighting white blood cells) which trigger the release of small proteins called cytokines. Other proteins such as bradykinin are also released. Bradykinin is a major trigger for early cold symptoms such as sore throat and nasal congestion. Cytokines such as interleukin-1 (IL-1) and interleukin-6 (IL-6) cause fever and chills in some people.
Then your symptoms start…
A sore throat is often the first symptom. The pain that you feel is due to the action of prostaglandins (hormones) and bradykinin (a protein) on sensory nerve endings in your upper airway. Pain signals are carried to your brain by cranial nerves in the area.
Sneezing is common. Inflammation in the nose triggers the trigeminal nerve to activate the “sneeze center” in the brainstem. The brain then triggers the sneeze reflex.
A runny nose is a frequent early symptom. The trigeminal nerve stimulates glands to release a clear nasal discharge. As the cold develops over days, the color of the nasal discharge may turn yellow and then sometimes green. The color change is due to the presence of increasing numbers of disease-fighting white blood cells in the fluid. The color comes from a green protein called myeloperoxidase which is contained in some of these cells. The color of the nasal discharge correlates with how much inflammation is going on in your body. This same rule applies to the sputum that you may cough up.
Sinus pain may occur. The maxillary sinuses, which are on both sides of the nose, often become inflamed and painful after the nasal congestion starts. Pressure increases in the bony spaces of the sinuses and the blood vessels near the sinuses also become congested. The sinus pain often worsens when you lie down due to pressure changes in the surrounding blood vessels.
Some individuals develop watery eyes. A small tunnel running from the nasal cavity and opening into the inner corner of each eye (known as the nasolacrimal duct) can become blocked due to the swelling and congestion in the lining of the nasal cavity. This causes tears to accumulate and you may develop watery eyes.
Then most people develop a nagging cough. This can last for several weeks, long after the other symptoms have resolved. Nasal irritation can cause sneezing but once the inflammation moves down to the larynx and closer to the lungs, a cough reflex is triggered. Inflammation of the lower airway lining can stimulate the vagus nerve which then transmits a signal to the cough center in the brainstem. Airway muscles contract and you cough. The cough reflex becomes overactive when you have a cold. When there is a lot of inflammation in the lower airway, you may also cough up yellow or green sputum. Unfortunately, a cough can sometimes last for several weeks after the other symptoms resolve.
Approximately 50% of adults with a cold also develop muscle aches. The inflammatory cytokines previously mentioned cause breakdown of skeletal muscle and can also trigger release of a hormone called prostaglandin E2. This hormone triggers peripheral pain receptors and muscle pain results.
Fever in adults with a cold is less common and more likely to occur if you are infected with influenza virus or by a virus that your body has never seen before. This explains why infants are more likely to have fever with any viral infection than adults. The common cold, often caused by rhinovirus, is not typically associated with fever although it can be. When you are infected, the inflammatory cytokines IL-1 and IL-6 send signals to the hypothalamus (the temperature control system in the brain). Your body temperature increases and you may start shivering. This explains why you may get a fever and chills with infection.
At this point there is no cure for the common cold. It can be due to one of several different viruses, most notably rhinovirus. Although the efficacy of the influenza vaccine changes every year, it usually decreases your risk of getting infected with influenza virus (“the flu”). I definitely recommend getting the flu shot every year. Unfortunately, there is no vaccine for rhinovirus or coronavirus yet, meaning that there is no shot that will prevent the common cold. Many people will still get a cold after getting the flu shot, but your chances of getting the flu will likely be lower.
If your symptoms follow the typical timeline of a common cold, there is a good chance that you have a rhinovirus or coronavirus infection that will get better over time without any specific treatment. Sometimes you need to wait for your own immune system to fight off the infection which typically takes 7-10 days.
Source:
Eccles, Ron. “Understanding the Symptoms of the Common Cold and Influenza.” The Lancet Infectious Diseases, vol. 5, no. 11, 2005, pp. 718–725., doi:10.1016/s1473-3099(05)70270-x.