Secondhand smoke exposure: health effects and how to protect yourself and children

ASH, a UK public health charity, describes breathing in other people's cigarette smoke as passive, involuntary or secondhand smoking. The smoke is a mixture of sidestream smoke from the burning tip of the cigarette and mainstream smoke that has been inhaled and exhaled by the smoker. ASH says nearly 85% of the smoke in a room comes from sidestream smoke, and that many potentially toxic gases are present at higher concentrations in it.

The particles include tar, nicotine, benzene and benzo(a)pyrene, and the gases include carbon monoxide, ammonia, formaldehyde and hydrogen cyanide. ASH says some have marked irritant properties and more than 50 are cancer-causing.

ASH lists short-term effects of exposure such as eye irritation, headaches, coughs, sore throat, dizziness and nausea. Adults with asthma can experience a significant decline in lung function when exposed, and short-term exposure has a measurable effect on the heart in non-smokers.

In the longer term, ASH reports increased risks across the smoking-related diseases. It cites a review by the Scientific Committee on Tobacco and Health that concluded exposure increases the risk of lung cancer in non-smokers by 24%, and estimates of a 25 to 35% increase in the risk of heart disease. It also reports links with stroke, with a strong dose-dependent association even at very low levels of exposure, and with breast cancer in non-smoking premenopausal women, as well as emerging evidence for dementia and for other conditions where it says further research is needed.

ASH notes that people particularly at risk include pregnant women and people with existing heart or respiratory illness.

ASH estimates that around 2 million children in the UK are regularly exposed to secondhand smoke at home, with many more exposed elsewhere. The risks ASH reports include the following.

• Cot death: the NHS says that exposing a baby to cigarette smoke can increase the risk of SIDS. ASH reports that having one or more smokers in the household more than doubles the risk of sudden unexpected death in infancy.

• Chest infections: ASH reports that exposure in the home increases young infants' risk of lower respiratory tract infections such as bronchitis and pneumonia by around 50%.

• Wheeze and asthma: ASH reports increased risks of wheeze and of asthma in children exposed before or after birth.

• Ear problems: ASH reports that exposure raises the risk of middle ear infection and glue ear.

• Meningococcal disease: ASH reports that exposure to smoke in the home more than doubles a child's risk of invasive meningococcal disease.

• Pregnancy: ASH reports that secondhand smoke exposure in pregnant women is associated with low birth weight, congenital anomalies and an increased risk of stillbirth.

ASH says opening a window or limiting smoking to a particular room offers little protection, and that smoking out of a window or next to an extractor fan is equally ineffective at keeping smoke out of the home. It reports that smoke from one cigarette can linger in a room for up to two and a half hours even with a window open.

It also describes emerging research on "thirdhand smoke": toxins from tobacco smoke that are absorbed by carpets, furnishings and walls and gradually released back into the air long after the smoke has dissipated.

ASH says the most reliable way of reducing children's exposure at home is for no one to smoke indoors at all, and that partial measures such as smoking in one room or not smoking when children are present are insufficient. If a parent cannot or will not stop smoking, its advice is that the next best step is to at least make the indoor environment smokefree.

The NHS advice on reducing the risk of SIDS is that you should not smoke when pregnant or around your baby after birth, and should not let anyone smoke in the same room as your baby. It also says not to share a bed with your baby if you or your partner smoke, no matter where or when you smoke.

The NHS runs stop smoking services and lists support including help to stop smoking in pregnancy and medicines to help you quit. ASH says the most reliable way to cut exposure is to stop smoking completely indoors.

According to ASH, smoking in all enclosed public places and workplaces was prohibited across the UK under the Health Act in 2007. In 2014 the Children and Families Act made it an offence to smoke in a private vehicle carrying children under 18 in England and Wales, and a similar law came into force in Scotland on 5 December 2016. ASH reports that Northern Ireland voted in favour of a similar ban in 2016.

ASH also says there are no laws that protect children from secondhand smoke in the home, which is why advice rests on voluntary measures and on support to quit. ASH's data is from a fact sheet dated March 2020, so check current rules if you need to rely on them.

If you or a child has persistent cough, wheeze, breathlessness or repeated chest or ear infections, see a GP, and tell them about smoke exposure at home because it can be a contributing factor. In an emergency such as severe difficulty breathing, call 999.

A GP, pharmacist or NHS stop smoking service can help anyone in the household who smokes to quit. NHS stop smoking services exist for this purpose, as the NHS quit smoking page sets out.