The "super cold" sweeping Britain is likely to be no worse than normal – but it is hitting people harder because of a lack of immunity.
Health experts said lockdowns, social distancing and masks had left Britons unable to shake off common infections.
Since last month, increasing numbers of people have reported symptoms ranging from sandpaper throats to muscle aches, with some saying their cold has left them exhausted or bedridden.
Official figures show the number of people coming forward with common colds and other respiratory infections is growing, particularly among the under-15s, although cases are also rising in older people.
But experts said the debilitating symptoms were being caused by a lack of immunity rather than a more virulent cold virus.
How to tackle a cold
Neil Mabbott, professor of immunopathology at the University of Edinburgh, said: "It is unlikely we are seeing the circulation of a ‘super cold’. Rather, our immune systems have had limited exposure to colds over the past 18 months, so our immunity to these will have waned and will be less effective against colds than would be expected normally.
"This highlights the power of the lockdown, mask-wearing, social distancing and sanitation measures introduced in response to the Covid-19 pandemic.
"Not only was this very effective in reducing transmission of the coronavirus within the community, but at the same time it had the additional benefit of reducing the spread of colds and other common transmissible diseases."
However, experts warned that some symptoms of colds and Covid can be similar and said it was important to get tested if a fever or cough develops or people begin to lose their sense of taste or smell.
Alan McNally, professor of microbial evolutionary genomics at the University of Birmingham, said: "If you have any symptoms of respiratory infection you should stay at home to prevent transmission and get a test done for Covid-19 to rule in or out.
"Trying to self-diagnose is a surefire way to send Covid-19 case rates soaring again."