Why does health advice change?

Sometimes health advice changes based on new research and evidence. This back and forth can make it seem like health experts are flip-flopping, when they are actually following scientific consensus.

For example, at the beginning of the COVID-19 pandemic, the Public Health Agency of Canada (PHAC) discouraged the use of masks on the advice of the World Health Organization (WHO). Once new evidence came to light that wearing masks could help stop the spread of the virus, PHAC recommended masks be worn when physical distancing was not possible.

What is scientific consensus?

Science is always changing and evolving. Scientific consensus means what the weight of evidence in a field suggests is most likely true. There can be consensus on a fact or on a theory (an explanation of how something works or why something happens).

There isn’t a consensus on every topic. Questions like what causes Alzheimer’s disease or the best way to treat injuries to the Achilles tendon are still unsettled.

It’s often easier to reach negative consensus: Scientists don’t know exactly what combination of factors causes autism, for example, but vaccines have been ruled out as a risk by comparing children who received vaccinations with those who didn’t to see if they were more likely to develop autism.

What are some examples of health advice that’s changed?

• Stomach ulcers are a good example of how changing consensus has changed medical advice. Doctors used to believe they were caused by stress and spicy food and prescribed antacids and a restricted diet. This reduced the symptoms but did not cure the ulcers.
• In the early 1980s, scientists discovered ulcers might be caused by bacteria and began to treat them with antibiotics. By 1990, antibiotics were part of the recommended treatment for stomach ulcers.

Why should we trust health and scientific experts on what they say now if the evidence is always changing anyway?

Trust is earned through expertise and effort. Modern medical advice is grounded in careful investigation and collaboration and takes time to develop.

Doctors and public health authorities draw on scientific consensus to make decisions about how to keep people healthy. If there is no clear consensus yet, they give advice based on the best available evidence.

Do Canadians trust their health experts?

Yes. According to research into the change in policy on masking during the COVID-19 pandemic, trust in public health officials is still consistent across Canada.

Another 2020 study showed that public health officials and physicians/nurses ranked highly with Canadians as trusted sources of information. Almost three-quarters of respondents agreed that “it is understandable that public health guidance will change as experts learn more about the coronavirus that causes COVID-19.’’