as of 2017 heated and humidified air, such as via rhinotherm, is of unclear benefit. one study has found chest vapor rub to provide some relief of nocturnal cough, congestion, and sleep difficulty. some advise to avoid physical exercise if there are symptoms such as fever, widespread muscle aches or fatigue. it is regarded as safe to perform moderate exercise if the symptoms are confined to the head, including runny nose, nasal congestion, sneezing, or a minor sore throat. there is a popular belief that having a hot drink can help with cold symptoms, but evidence to support this is very limited. antibiotics and antivirals antibiotics have no effect against viral infections, including the common cold. due to their side effects, antibiotics cause overall harm but are still frequently prescribed. some of the reasons that antibiotics are so commonly prescribed include people's expectations for them, physicians' desire to help, and the difficulty in excluding complications that may be amenable to antibiotics. there are no effective antiviral drugs for the common cold even though some preliminary research has shown benefits. zinc main article: zinc and the common cold zinc supplements may shorten the duration of colds by up to 33% and reduce the severity of symptoms if supplementation begins within 24 hours of the onset of symptoms. some zinc remedies directly applied to the inside of the nose have led to the loss of the sense of smell. a 2017 review did not recommend the use of zinc for the common cold for various reasons; whereas a 2017 and 2018 review both recommended the use of zinc, but also advocated further research on the topic. alternative medicine while there are many alternative medicines and chinese herbal medicines supposed to treat the common cold, there is insufficient scientific evidence to support their use. as of 2015, there is weak evidence to support nasal irrigation with saline. there is no firm evidence that echinacea products or garlic provide any meaningful benefit in treating or preventing colds. vitamins c and d main article: vitamin c and the common cold main article: vitamin d and respiratory tract infections vitamin c supplementation does not affect the incidence of the common cold, but may reduce its duration. there is no conclusive evidence that vitamin d supplementation is efficacious in the prevention or treatment of respiratory tract infections. prognosis the common cold is generally mild and self-limiting with most symptoms generally improving in a week. in children, half of cases go away in 10 days and 90% in 15 days. severe complications, if they occur, are usually in the very old, the very young, or those who are immunosuppressed. secondary bacterial infections may occur resulting in sinusitis, pharyngitis, or an ear infection. it is estimated that sinusitis occurs in 8% and ear infection in 30% of cases. epidemiology the common cold is the most common human disease and affects people all over the globe. adults typically have two to three infections annually, and children may have six to ten colds a year (and up to twelve colds a year for school children). rates of symptomatic infections increase in the elderly due to declining immunity. native americans and inuit are more likely to be infected with colds and develop complications such as otitis media than caucasians. this may be explained as much by issues such as poverty and overcrowding as by ethnicity. history a british poster from world war ii describing the cost of the common cold while the cause of the common cold was identified in the 1950s, the disease appears to have been with humanity since its early history. its symptoms and treatment are described in the egyptian ebers papyrus, the oldest existing medical text, written before the 16th century bce. the name "cold" came into use in the 16th century, due to the similarity between its symptoms and those of exposure to cold weather. in the united kingdom, the common cold unit (ccu) was set up by the medical research council in 1946 and it was where the rhinovirus was discovered in 1956. in the 1970s, the ccu demonstrated that treatment with interferon during the incubation phase of rhinovirus infection protects somewhat against the disease, but no practical treatment could be developed. the unit was closed in 1989, two years after it completed research of zinc gluconate lozenges in the prevention and treatment of rhinovirus colds, the only successful treatment in the history of the unit. research directions antivirals have been tested for effectiveness in the common cold; as of 2009, none had been both found effective and licensed for use. there are ongoing trials of the anti-viral drug pleconaril which shows promise against picornaviruses as well as trials of bta-798. the oral form of pleconaril had safety issues and an aerosol form is being studied. double-stranded rna activated caspase oligomerizer (draco), a broad-spectrum antiviral therapy, has shown preliminary effectiveness in treating rhinovirus, as well as other infectious viruses. the genomes of all known human rhinovirus strains have been sequenced. societal impact the economic impact of the common cold is not well understood in much of the world. in the united states, the common cold leads to 75–100 million physician visits annually at a conservative cost estimate of $7.7 billion per year. americans spend $2.9 billion on over-the-counter drugs and another $400 million on prescription medicines for symptom relief. more than one-third of people who saw a doctor received an antibiotic prescription, which has implications for antibiotic resistance. an estimated 22–189 million school days are missed annually due to a cold. as a result, parents missed 126 million workdays to stay home to care for their children. when added to the 150 million workdays missed by employees who have a cold, the total economic impact of cold-related work loss exceeds $20 billion per year. this accounts for 40% of time lost from work in the united states.