Is there a safe level of secondhand smoke?

Health Canada says there is no safe level of exposure to second-hand smoke.

What does secondhand smoke do to children?

Health Canada lists sudden infant death syndrome, respiratory illness, ear infections and more severe asthma attacks, and says exposure after birth can affect infant brain and lung development.

Does opening a window or running an air purifier help?

Health Canada says cleaning or filtering indoor air, more ventilation and separate smoking areas do not eliminate exposure or the health risks. The only solution it names is eliminating smoking in enclosed spaces.

What Does Secondhand Smoke Do to Your Health?

What secondhand smoke is

Health Canada says second-hand smoke contains more than 70 cancer-causing chemicals. Those chemicals are many of the same ones found in the smoke a smoker inhales, so a person who never lit a cigarette can still take them in.

The headline numbers

Health Canada’s page gives a few figures worth keeping in mind:

Second-hand smoke was responsible for 993 deaths in Canada in 2012.
An estimated 22% of Canadian non-smokers are exposed every day or almost every day.
Non-smokers who live with someone who smokes have a 30% increased risk of lung cancer, heart disease and stroke.
In 2015 it caused 429 of 7,112 new lung cancer cases and 131 of 926 new cervical cancer cases.

The page’s own statement is blunt: “There is no safe level of exposure to second-hand smoke.”

Children and infants

Children have the highest measurable exposure among people exposed at home, according to Health Canada. The risks it lists:

Second-hand smoke is a major risk factor for sudden infant death syndrome.
Infants and children exposed have a higher risk of respiratory illness and ear infections.
It can cause more severe asthma attacks in children who have asthma.
Exposure after birth can affect infant brain and lung development.

Cars are the sharpest example. Health Canada reports that 26% of youth were exposed to second-hand smoke in a vehicle in 2016-2017, and that concentrations in vehicles can be much higher than in other enclosed spaces. That is why every province and territory bans smoking in vehicles with minors; Ontario’s limit is passengers aged 15 or younger and Saskatchewan’s is under 16, and the full list is in smoking in a car with children.

Adults

For adults, the findings centre on the heart and lungs. Health Canada notes that second-hand smoke contributes to blood clots in blood vessels, which in turn contribute to heart disease and stroke, and that the chemicals can contribute to tumour formation in the lungs.

Pregnancy

Health Canada’s page on second-hand smoke does not set out risks to pregnant women, and we do not cite figures here. It does say that exposure after birth can affect infant development. If you are pregnant or planning to be, ask your doctor, midwife or provincial health line, and see quitting smoking while pregnant.

What does and does not reduce exposure

Health Canada is clear that cleaning or filtering air, increasing ventilation and using segregated smoking areas do not eliminate exposure or the associated risk. “The only solution is to eliminate smoking in all enclosed spaces,” it says, and it names vehicles and homes specifically.

In practice:

Make the car and home smoke-free, with no exceptions for open windows.
If you live in a building where smoke drifts between units, see the tenants’ guide for what you can ask your landlord to do.
If someone in your household smokes, quitting at any age reduces the risk of premature death, according to Health Canada. Free counselling is available in every province and territory.

Residue left behind on surfaces after smoking is a separate and less settled topic, covered in thirdhand smoke.

This page is general information, not medical advice.

Health information is general and educational. It does not replace advice from a doctor, pharmacist or nurse. Read the full disclaimer.

Secondhand Smoke: Health Effects and Exposure

Key takeaways