The common cold is indeed common. It can be caused by more than a hundred different viruses (primarily rhinovirus).
Flu (influenza) is caused by an infection of types A, B or rarely C influenza viruses. Types A and B can cause severe illness and even death. Type A has caused serious pandemics.
In an article of ours (Reid, Taylor & Walf, 2019), we provided evidence that taking over-the-counter common cold medicines might be more harmful than beneficial. In brief, the common ingredient in these “medicines” tends to disable the immune system of the airway, reducing its ability to fight infections.
Many retail stores sell a large array of drugs purported to cure or shorten the duration of a common cold. Research indicates that these drugs reduce some symptoms of a cold, but in so doing may put citizens at risk of other infectious diseases.
Both cold and other viruses can infect the airway. Now, there is the novel virus of COVID-19.
There are important differences between the cold and flu viruses, even though they share some symptoms. Cold viruses can cause an infection that is uncomfortable and lasts about 10 days. Colds are almost always cured by our innate immune system of the respiratory mucosa without any drug-intervention. On the other hand, Flu viruses can cause very serious infections, and if not controlled can be fatal.
There is a misinformation problem – when a citizen has cold or flu-like symptoms, they buy a drug advertised to treat cold and flu, believing that it will stop the progression of the Flu, which it will not. The active ingredients in these medicines can temporarily mask flu symptoms and delay getting an anti-viral drug (which can be a fatal mistake).
Vaccinations for the Flu might not be effective every Flu-season, and if that happens many will buy an OTC drug with a label for “For Cold and Flu,” however, that is a false label, a false inducement to buy a cheaply made product with a high profit margin.
Below is a Table from Illinois Public Health. The columns depict whether a symptom is rare or not. We add that the high temperature associated with Flu can be accompanied with chills. Fever with chills is a major symptom of Flu. Also, symptom onset is abrupt with the Flu but more gradual with a Cold. Anti-viral medicines should be given quickly when major symptoms manifest to prevent life-threatening complications. It can be serious problem when a drug can be purchased without a prescription and is advertised as a medicine for both a common Cold and Flu.
Now, there is COVID-19. The general population is apt to take a drug designed to reduce the symptoms of a common cold which are similar to the very early symptoms of both a common cold and the virus of COVID-19. It they do that, and have infections associated with COVID-19, they may hinder the natural immune processes that will fight the disease. We do not recommend drugs to treat the symptoms of a common cold and do recommend when symptoms (particularly fever) of flu and COVID-19 infections occur to immediately seek advanced medical care. Soon after an infection of the COVID-19 virus, there is a fever, cough, sore throat, congestion, and difficulty breathing.