The World's Most Common Illness
The common cold is the most common human disease, found all over the world. The average adult gets two to three colds a year, and children may get six to eight.
It is an infection of the upper respiratory tract: the nose, throat, sinuses and voice box. Symptoms can start within 16 hours of catching it and usually peak two to four days later. They include a runny nose, sneezing, a sore throat, coughing, headaches and tiredness.
Most people recover in seven to ten days, though some symptoms can hang around for up to three weeks. A cough lasts 18 days on average.
Here is a surprise: the symptoms are not mainly caused by the virus damaging your body. They come mostly from your own immune response, your body's reaction as it fights the infection.
And the colour of your mucus, whether clear, yellow or green, does not tell you whether an infection is caused by a virus or by bacteria.
More Than 200 Culprits
Colds are caused by viruses, and there are a lot of them. More than 200 types have been linked to colds. The most common cause is the rhinovirus, behind up to 40 percent of cases, and it alone comes in over 100 varieties. Others include coronaviruses and adenoviruses.
Colds spread through tiny droplets released when someone breathes, talks or coughs, or through touching contaminated objects. Rhinoviruses can survive on surfaces for more than 18 hours, so a hand can pick one up and carry it to the eyes or nose.
Children spread them easily. Daycare centres and schools bring together lots of children with little immunity, and they carry the infections home to their families.
What about cold weather? It is a common myth that simply being cold gives you a cold. Colds are caused by viruses, not temperature. But they are more common in winter. The reasons are not fully known, but they may include people spending more time indoors together, and dry air helping droplets spread further.
Why There Is Still No Cure
There is no vaccine for the common cold. Too many different viruses are involved, and they change quickly, so creating one vaccine that works against them all is extremely unlikely.
There is no cure either. Treatments can only ease the symptoms. Rest, drinking fluids and gargling with warm salt water are sensible steps, but much of the benefit of cold remedies is thought to come from the placebo effect.
An antibiotic will not help at all, because antibiotics kill bacteria, not viruses. Yet they are still often prescribed for colds, which helps bacteria become resistant to them.
A few things may help a little. Zinc taken within 24 hours of symptoms starting may shorten a cold by up to 33 percent. Taking vitamin C regularly does not stop you catching colds, but may make them slightly shorter. There is no firm evidence that echinacea or garlic help.
The best protection is simple: wash your hands properly and keep away from people who are sick.
An Ancient Illness With a Modern Price
Colds have been with humans throughout history. Their symptoms and treatment are described in the Ebers papyrus from ancient Egypt, the oldest existing medical text, written before the 16th century BCE.
The name cold came into use in the 16th century, because its symptoms seemed similar to those of being out in cold weather.
Finding the cause took a long time. In 1946, Britain set up the Common Cold Unit to study the illness, and it was there that the rhinovirus was discovered in 1956. The unit closed in 1989, two years after testing zinc lozenges, the only successful treatment in its history.
Even such a mild illness costs a great deal. In the United States, colds lead to 75 to 100 million doctor visits a year. Counting missed work, including parents staying home with sick children, the cost of lost working time is more than 20 billion dollars a year.
