The common cold is not actually a single disease. A cold is a viral infection of the upper respiratory tract – that is your mouth, nose, sinuses and throat – and there are well over 200 different virus strains that can make you ill.
The most common of these strains are called rhinoviruses, from the Greek for nose, and they account for up to 75% of colds in adults. Other varieties include coronaviruses, adenoviruses and coxsackieviruses. But each and every one of them causes the symptoms of a cold that we are all too familiar with – a blocked or runny nose, a sore throat, headaches, sneezing and a cough.
Why is that?
To understand what causes a cold and why we get sick, we need to first understand how we catch a cold virus and then how our body’s defense mechanism responds to it.
How we catch a cold
Cold viruses are spread from person to person through tiny drops of liquid. If someone who is sick coughs or sneezes, microscopic virus-containing droplets are sprayed into the air. When these settle on a surface, such as a table, door handle or even a smartphone, the virus can survive there for several hours.
If you then touch one of these surfaces, the virus can transfer to your hands and ultimately spread to your nose or mouth. Similarly, if someone who is ill touches their mouth or nose and then an object, the virus can be transmitted by you subsequently touching it.
Once in your nose or mouth, the virus binds to the cell lining and starts replicating. Unlike bacteria, which has a cellular structure, viruses are much smaller and can only reproduce inside the living cells of other organisms. As they spread from cell to cell in your upper respiratory tract, your body begins to fight back.
How your body battles back
The reason that you feel ‘sick’ and suffer the symptoms associated with a cold are not actually the direct effect of the virus. It is the result of your immune response to it.
When a virus is detected, the affected cells send out tiny protein messages called cytokines prompting your immune system to kick into gear. The blood vessels inside your nose and throat swell enabling more blood to flow to the infected area and send white blood cells to fight it. At the same time, your mucus production goes into overdrive.
Even when you are healthy, mucus plays a vital role in lubricating and filtering your respiratory tract. As well as keeping the cell lining from drying out, mucus traps undesirable substances like dust and bacteria from entering the body. It also contains antibodies that can attack any bacteria or viruses it has ensnared. So, by increasing your mucus when you are ill, your body is working to trap both the virus and the dead white blood cells that have been fighting it and then flush them away.
But these defense mechanisms come with a downside, they cause the symptoms we associate with a cold. Increased mucus and an inflamed nasal lining cause your nose to be blocked. Similarly, thick excess mucus can build up and clog your sinuses causing congestion, headaches and infections.
When this mucus drains down from your nose to your throat, known as postnasal drip, it can cause you to have a sore throat. And as it moves towards your lungs, you can develop a cough as you try to clear your airwaves. Both a sore throat and a cough can also be triggered by the lining of your respiratory tract becoming irritated or inflamed in response to the virus.
Can you prevent getting sick?
Adults catch on average two to four and children between six and ten colds every year. With something this common, you might wonder why a cure hasn’t been developed. Because there are so many strains of cold viruses out there, and because they can mutate frequently during reproduction, it is an extraordinarily difficult task to find a vaccine that would be universally effective.
This is in contrast to the ‘flu’. There are four main types of influenza virus, so the customized vaccines developed each year can provide pretty good protection to vaccinated people. We also cannot use common antibiotics to fight the primary cold as they only work on bacterial infections. Those types of illnesses can happen following a viral one.
So, while we may not be able to avoid getting a cold completely, there are things you can do to both lessen the risk of catching one and reduce the severity of the symptoms if you do get sick:
1. Keep your defenses up
- Maintaining a healthy immune defense system can lower the incidence, severity and duration of the common cold. Alongside a healthy, active lifestyle, taking certain vitamin supplements may help in preventing and treating cold viruses.
- Vitamins C and zinc, in particular, are often recommended to help fight illness. But this view is not without controversy. There have been a huge number of studies into their efficacy and scientists still differ on how beneficial they are (especially vitamin C).
- Meta-studies that combine all the results from other research, however, do suggest that together, vitamin C and zinc could make a tangible contribution to lessening the severity of the symptoms and speeding up the recovery in cold sufferers. And this is especially important for those groups most at risk from getting ill, such as the elderly, children and pregnant women.
2. Keep your hands clean and stay healthy
- We know that most colds spread through touch and people frequently touch their eyes, nose, and mouth without even realizing it, so making sure you thoroughly wash your hands is a must. And it is even more effective than you might think.
- Handwashing helps reduces respiratory illnesses, such as colds, in the general population by up to 21%. While a study in the UK in 2015, found that using soap and water or hand gel not only reduced the number of cases of colds and flu, but the severity of symptoms and the length of time people were ill.
3. Think fast, the first 12 hours are key
- If you start to feel you are getting a cold, the quicker you act the better. Making sure you can breathe through your nose by reducing the build-up of thick mucus can both lessen the risk of infection and reduce the severity of any symptoms.
- Decongestants sprays or tablets can clear a stuffy nose through shrinking swollen blood vessels, while inhaling steam (either in the shower or over a bowl of hot water) can thin and loosen mucus. Gargling salt water can also reduce the build-up of excess mucus in your throat.