A quarter of people wrongly believe antibiotics work on most coughs and colds, a Health Protection Agency survey has found.
However antibiotics cannot treat viruses, which cause most respiratory tract infections.
The HPA poll of 1,800 people in England also found one in 10 people keep leftover antibiotics - and many would self-medicate next time they got ill.
A leading GP said antibiotics were not a "cure all".
An expert in immunity and infection is also warning that the misuse of antibiotics, and drug companies' failures to develop new ones, could lead to a rise in untreatable infections.
The European Centre for Disease Prevention and Control said that antimicrobial resistance "is one of the most serious public health challenges that we face in the EU" and could cost at least 1.5bn euros.
Speaking on European Antibiotics Awareness Day, the HPA's Dr Cliodna McNulty said self-medicating was unsafe and could fuel drug resistance.
Dr McNulty, head of primary care for the HPA, said: "The majority of people can treat themselves at home using over-the-counter medicines to relieve symptoms." more