Dr. Theresa Tam provided the updated advice during her daily news conference in Ottawa today.
"For the spring and summer months, strict adherence to the public health basics of physical distancing, handwashing and cough etiquette must continue as the bare minimum," she said.
"In addition, where COVID-19 activity is occurring, use of non-medical masks or face coverings is recommended as an added layer of protection when physical distancing is difficult to maintain. And staying home when sick is a must, always and everywhere."
Tam said the new guideline comes as provinces begin to allow businesses and services to reopen, bringing more people out of their homes.
Asked if the recommendation should have come earlier in the pandemic emergency, Tam said public health advice has been evolving based on the science. That advice is also now responding to the fact that, with more provinces taking cautious steps toward reopening their economies, more Canadians are coming into closer proximity to one another in public.
"We need to flexibly change our measures as we get more information," she said.
Tam said the advice coming from her office today is a "specific recommendation," while the previous language was "more permissive."
The position taken by Tam's office at the start was that masks can protect others — so if someone is showing symptoms and needs to go out, they need to cover their face. As officials learned more about asymptomatic and pre-symptomatic carriers and their potential role in transmission, the advice on masks changed.
Asked if the federal government could issue a directive to make mask-wearing in public mandatory, Tam said it remains a recommendation at the national level — but provinces and communities could make their own decisions based on local conditions.
She also warned that wearing a mask won't protect an individual from infection on its own, and stressed that physical distancing remains fundamental.
Tam said measures to suppress the disease through the summer are essential to buy more time for research and innovation on medical therapies and vaccine development.
Earlier today, Prime Minister Justin Trudeau said he has started wearing a mask in public in situations where he could be in close proximity to people.
"That's my personal choice. I think that's what is aligned with what public health is recommending," he said. "I think we all need to adjust to what works in our circumstances and keep safety at the forefront of what we're doing."
Trudeau said he will wear a mask to in-person sittings of Parliament but will remove his mask once at his desk to engage in parliamentary debate.
He was first seen wearing a mask in public during a May 6 Canadian Armed Forces repatriation ceremony.
Trudeau said again that the best measures to limit the spread of COVID-19 are to stay two metres apart, to stay at home whenever possible and to wash hands regularly and frequently.
Singh following health advice
NDP Leader Jagmeet Singh will be wearing a mask outside of his home "in times when physical distancing is hard or not possible," says a statement from his office.
"From the beginning of this crisis, he had followed public health experts' advice and will continue to do so," says the statement.
Asked if Conservative Leader Andrew Scheer is wearing a mask, a party spokesperson said: "A number of our MPs have made the personal decision to wear masks on the Hill. Conservative MPs will continue to follow public health guidelines."
The World Health Organization (WHO) has not formally recommended wearing masks and has said the evidence is inconclusive on whether people who are asymptomatic should wear them.
But many experts say masks should be mandatory because they can reduce the amount of airborne droplets that can carry the virus.
Several countries, including Spain, have made wearing masks compulsory in cases where the two-metre physical distancing rule can't be observed.
Today, Ontario's provincial government said passengers on public transit should wear masks.