Many people believe vitamin C can cure the flu and echinacea can prevent colds. But is there scientific evidence to back this up?
Can vitamin C stop a cold?
"Research has found no evidence that vitamin C prevents colds," says Dr Hasmukh Joshi, vice-chair of the Royal College of General Practitioners.
In 2013, an updated review of studies into vitamin C and the common cold concluded that "regular ingestion of vitamin C had no effect on common cold incidence in the ordinary population".
The review results suggested that vitamin C might help prevent colds in people exposed to short periods of intense physical activity, such as marathon runners or skiers, but not in the general population.
A daily dose of vitamin C did slightly reduce the length and severity of colds in the ordinary population.
When it comes to flu, one person in three believes that taking vitamin C can cure the flu virus. It can’t.
"Studies found that vitamin C offers a very, very limited benefit," says Dr Joshi. "I wouldn't recommend it."
Does echinacea reduce cold risk?
The root, seeds and other parts of echinacea plants are used in herbal remedies that many people believe protect them against colds. There have been several studies into echinacea’s effect, but no firm conclusions.
A 2013 update of a review of trials on echinacea and the common cold found that echinacea products were not shown to provide benefit in treating colds overall, but that it was possible there is a weak benefit from some echinacea products.
The review found that trials looking at whether echinacea prevents colds showed positive, but non-significant, results.
The studies reviewed had varying results and used different preparations of echinacea. It’s not known how these compare with the echinacea in shops.
"There is a belief that echinacea aids the immune system, but a survey of studies in 2005 showed that it did not," says Dr Joshi. "I wouldn't recommend that it helps, but if people believe it, they can take it."
Echinacea should not be given to children under 12 years old.
Find out more about a study of echinacea published in 2012 at Echinacea cold study claims analysed.
Will zinc put off a cold?
There is some evidence that taking zinc (in lozenges, tablets or syrup) may reduce how long a cold lasts.
A 2013 update of a Cochrane review of studies into zinc and the common cold suggests that taking zinc supplements within 24 hours of the symptoms starting will speed up recovery from a cold and lessen the severity of symptoms in healthy people.
Long-term use of zinc isn't recommended as it could cause side effects such as nausea and a bad taste in the mouth. More research is required to find out the recommended dose.
There has also been research into nasal sprays containing zinc. "Some people believe that the zinc lines the mucosa [the lining of the nose] and stops a cold virus attaching itself to the nose lining," says Dr Joshi. "Unfortunately, this has been found to be no more effective than a placebo."
Does getting cold or wet cause colds?
The only thing that can cause a cold or flu is a cold or flu virus. Getting cold or wet won’t give you a cold. However, if you are already carrying the virus in your nose, it might allow symptoms to develop.
A study at the Common Cold Centre in Cardiff found that people who chilled their feet in cold water for 20 minutes were twice as likely to develop a cold as those who didn't chill their feet.
The authors suggest that this is because some people carry cold viruses without having symptoms. Getting chilled causes blood vessels in the nose to constrict, affecting the defences in the nose and making it easier for the virus to replicate.
"Getting a cold from going out in the cold or after washing your hair is a myth," says Dr Joshi. "Colds are common. If the virus is already there and then you go out with wet hair and develop symptoms, it's common to think that is what caused it."
So what does work to prevent colds and flu?
The flu vaccine can prevent you from catching flu. Apart from that, the best way to protect yourself from colds and flu is to have a healthy lifestyle.
"Eat a healthy diet, take regular exercise and drink plenty of warm drinks in the winter months," says Dr Joshi. "The important thing to remember is that most people are going to catch a cold in winter anyway, because there is no effective cure for cold viruses."
Washing your hands will help avoid transmitting cold and flu viruses
Cold and flu viruses can be passed through tiny droplets of mucus that are sneezed or coughed out into the air by an infected person, and breathed in by another person.
If an infected person sneezes into their hand, and then touches an object (such as a doorknob, or railing on a train) the virus can pass from the object to the next person who touches it.
By washing your hands, you will be getting rid of any viruses you've picked up on them.
Avoiding touching your nose and eyes will help stop you getting infected
Cold and flu viruses can enter your body through the eyes and nose. If you have any infected droplets on your hands, and you touch your eyes or nose, you can pass the virus into your system.
By not touching your nose and eyes, you'll reduce your chances of catching a virus.