People are more susceptible to infections in the mornings than at the end of the day, new research has found.

Experts at Cambridge University in the U.K. found flu, the cold sore virus and other germs are more likely to strike when the body clock is out of sync, meaning those on shift work or changing their working hours could be at risk.

Researchers believe viruses’ abilities to spread and breed is affected by internal clocks and changes to our body that come with getting older. The way germs live and thrive is by taking over our cells and changing the way they format. Cells are at their busiest in the morning, therefore if a virus strikes then, it’s easier for it to take over.

To come to their conclusion experts infected mice with herpes at different times in the day, noting how it multiplied 10 times as quickly in the mice given the bug at sunrise than those infected later in the day. The bug spread even faster when given to mice with no body block gene.

“This indicates that shift workers, who work some nights and rest some nights and so have a disrupted body clock, will be more susceptible to viral diseases,” first author Dr Rachel Edgar said.

The findings also suggest washing hands and steering clear of ill people will be more beneficial in the mornings. It was further discovered that body clocks change over the course of a year as well as a day, a reason why colds and the flu are more common in the colder months.

“The time of day of infection can have a major influence on how susceptible we are to the disease, or at least on the viral replication, meaning that infection at the wrong time of day could cause a much more severe acute infection,” Akhilesh Reddy, the study’s senior author, added.

“This is consistent with recent studies which have shown that the time of day that the influenza vaccine is administered can influence how effectively it works.”

The research was published in the journal Proceedings of the National Academy of Sciences.

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