A Cold: What Shortens One, What Only Feels Like It Does, and Why Antibiotics Are Never the Answer

The common cold is caused by more than two hundred viruses, most of them rhinoviruses, which is why there is no vaccine and why having one confers no protection against the next. It lasts seven to ten days in adults, a little longer in children and smokers, and it is self-limiting: the immune system clears it whatever you do. That is the frame for every remedy claim, because a treatment taken on day three of an illness that ends on day eight will always appear to work. The NHS advice is rest, fluids and painkillers, and the reason it is so short is that little else has survived a trial.

What has some evidence

Zinc lozenges, started within 24 hours of the first symptoms and taken every few hours through the day, shortened colds by a day or two in several trials, though the studies are small and mixed and the lozenges taste of metal and can upset the stomach; zinc nasal sprays should be avoided, since some caused permanent loss of smell. Honey, a spoonful at bedtime, reduces night-time cough in children over one and probably in adults, and does so better than most over-the-counter cough medicines in head-to-head trials; it must not be given to infants under twelve months. Saline nasal rinses and sprays clear congestion mechanically and are safe for anyone. Paracetamol and ibuprofen treat the headache, the sore throat and the aches, and neither shortens the illness. Steam inhalation feels good and the trials are negative; it is harmless unless the bowl tips. Decongestant tablets and sprays open the nose for a few hours; sprays used more than three days cause rebound congestion that is worse than the cold.

What does not

Vitamin C taken once a cold has started does nothing measurable. Taken daily all year it reduces the duration of colds by about eight per cent in adults, which is a few hours, and only clearly reduces the number of colds in people under heavy physical stress such as marathon runners and soldiers in the Arctic. Echinacea has been tested many times with results that cluster around zero. Garlic, elderberry and vitamin D each have a trial or two in their favour and larger ones against. Antihistamines do not help a cold unless there is an allergic component, and the sedating ones simply make you sleep, which is not nothing but is not treatment. "Cold and flu" combination products contain a painkiller, a decongestant and often caffeine; they are convenient and no more effective than the components bought separately, and they make it easy to double-dose paracetamol by taking them alongside plain tablets.

Antibiotics

Colds are viral and antibiotics act on bacteria; they do nothing for a cold, cause side effects in a fifth of those who take them, and drive resistance. Green mucus is not a sign of bacterial infection; it is a sign of white cells doing their job. The situations that do need a doctor are a fever that persists past a few days, ear pain in a child, breathlessness, a sore throat with white patches and no cough, symptoms that improve and then sharply worsen, which can mean a secondary sinus or chest infection, and any cold in someone with a serious lung or heart condition or a weakened immune system.

What actually helps

Rest. Sleep is when the immune response is most active, and people who sleep less than six hours catch more colds and clear them more slowly; a day off in bed on day two shortens the week more than any lozenge. Fluids, because fever and a running nose lose them, and warm ones because they soothe. Not spreading it: a cold is most infectious in the first three days, spreads by hands more than by air, and the single measure with the best evidence for preventing colds in a household is washing hands. The NHS sleep guidance is the least glamorous remedy on the list and the one that works. Our piece on dry indoor air covers the comfort side of a winter in heated rooms. Everything else is the passage of time, which a cold makes feel longer than it is.