Passive smoking and secondhand smoke: health risks and how to protect others

Passive smoking, also called secondhand smoking, means breathing in other people's tobacco smoke. Cancer Research UK explains that this smoke comes from burning tobacco, including cigarettes, pipes, cigars and shisha pipes, and that it consists of the smoke the person breathes out and the smoke from the burning end of the tobacco.

Tobacco smoke contains over 5,000 chemicals, many of which are harmful and some of which can cause cancer. Secondhand smoke is not the same as vapour from e-cigarettes, which the charity treats separately.

The smoke can also settle. Cancer Research UK says it builds up on surfaces, furniture and clothes, and refers to this as third hand smoke. That is one reason a home where people have smoked can remain a source of exposure even when nobody is smoking at that moment.

Cancer Research UK says passive smoking can cause lung cancer, heart disease and stroke, and may increase the risk of other cancers, such as breast cancer, and of chronic obstructive pulmonary disease (COPD). In the short term it can cause coughing, headaches, a sore throat and eye and nose irritation.

The British Heart Foundation similarly says secondhand smoke is harmful and increases the risk of breathing problems, cancers such as lung cancer and cardiovascular disease such as stroke and heart attack in the people breathing it in.

These risks matter at home, in shared vehicles and at work in places where smoking is still allowed.

Children and babies are more vulnerable because their lungs and immune systems are still developing. Cancer Research UK lists asthma, bacterial meningitis, cot death, middle ear infection and respiratory infections as conditions they are at higher risk of. The British Heart Foundation says children who live in a home with smokers can have double the risk of illnesses such as pneumonia, ear infections, wheezing and asthma.

During pregnancy, Cancer Research UK says secondhand smoke can have serious risks for the baby during pregnancy and after birth, including an increased risk of low birth weight and cot death. It says it is not yet clear whether there is a link between exposure before birth and childhood cancer.

The charity also notes that the dangers of smoking around children go beyond smoke itself: children with family members who smoke are more likely to start smoking themselves.

Cancer Research UK says the only way to protect loved ones is to keep the environment around them smoke free. Smoking in certain rooms or opening a window is not enough, because smoke spreads from room to room and can stay in the air for hours. The best way to keep a home smoke free is to stop smoking completely.

Until you stop, the charity advises always smoking outside and away from the house, and asking visitors to do the same. Never smoke in the car or let anyone else do so, because smoke can reach very high levels in a small enclosed space even with the windows open. In the UK it is against the law to smoke in a vehicle with anyone under 18 inside.

• Make your home and car completely smoke free.

• Ask visitors to smoke outside, away from doors and windows.

• Use free NHS stop smoking support to quit for good.

The NHS says local stop smoking services are free, and offer advice, professional support and access to treatments such as nicotine replacement therapy and stop smoking tablets. A GP, pharmacist or health visitor can refer you, or you can contact your local service directly.

If you are the person being exposed rather than the person smoking, it can feel awkward to raise it. Many people find it easier to frame it around a child, a pregnancy or a health condition, and to offer practical help, such as sharing information on free support.