As the days get shorter and the mornings get colder, there's a tendency to exercise less, sleep longer and spend more time at home.
These factors lead to what Swinburne University of Technology professor Greg Murray calls "the winter blues".
Murray is head of psychological sciences and statistics, and said there many factors that led to people being more sluggish and less productive in winter but there were practical ways to stay happy and healthy.
What are the winter blues?
Murray said life was just a bit harder in winter.
"We as human beings do find winter a bit challenging," Murray said.
"We might get physically sick but other things happen as well -- we may exercise less, socialise less, most of us do feel the need to sleep more so it's harder to get out bed."
Is that Seasonal Affective Disorder?
Murray said there was a distinction between a case of the blues and the more serious Seasonal Affective Disorder (SAD).
"It's hard to talk about a psychological response to winter without people thinking about SAD or winter depression," Murray said.
"SAD is variant of recurrent depression where people meet the criteria for episodes of clinical depression and those periods occur... linked to a particular season."
Murray said about one in 300 Australians had SAD but winter blues was much more common, and often wasn't diagnosed.
How do I avoid the winter blues?
Murray said the key to staying happy through winter was to make plans as soon as the weather changed.
"For people who have noticed pattern in their lives who tend to have a lowered mood in winter, there are common sense things to prepare," Murray said.
1. Get social. While it's still (relatively) warm, book in a friend to come over to dinner in July, or as Murray puts it: "slot in social events you can't get out of".
2. Get a short gym membership. Murray said a lot of people found they didn't need any impetus to exercise in spring or summer, but a membership or indoor exercise class through winter helped to keep people active.
"Try and invite a friend to exercise with once a week," he said.
3. Don't be too hard on yourself at work. Murray said you should expect to be less productive in winter when taking into account increased sick days for you and your team.
"It's not most productive or satisfying months on the calendar," Murray said.
"Cut yourself a bit of slack."
How do I stay well?
Monash Infectious Diseases infection prevention director Rhonda Stuart said flu vaccination was key.
"There's still time to get a vaccination for this year," Stuart said.
She also reminded people to wash their hands regularly and avoid touching your face, especially after being in public places or around sick people.
As well as that, Stuart said anyone who already had a cold should stay home form work and practice "cough etiquette" to make sure it's not spread further.
"Cough into a tissue," Stuart said.
"It can be hard to stay home from work when you know your colleagues will share your workload but... it's important you don't spread a cold or flu further."