Smoking - and breathing in other people's smoke - makes asthma worse over the long term by causing permanent damage to the lungs. It can also trigger asthma symptoms or even an asthma attack in the short term - 82 per cent of people with asthma tell us that tobacco smoke affects their asthma.
It's not just the smoke from cigarettes that causes a problem. The smoke from cigars, pipes, and hand-rolled cigarettes also puts dangerous pollutants into the air we breathe.
What is second-hand smoke?
When someone smokes they breathe smoke into their lungs. This is known as 'mainstream' smoke. Mainstream smoke, and all the chemicals in it, gets absorbed into the blood stream and body tissue. Some of this mainstream smoke is exhaled.
'Sidestream' smoke is the smoke given out by the lit end of the cigarette. Sidestream smoke gives out more than half of all the pollution given out by a cigarette.
Second-hand smoke is a combination of the mainstream smoke breathed out by the smoker, and the sidestream smoke coming out of the lit end of their cigarette.
Who is most likely to have second-hand smoke as a trigger?
Anyone with asthma or other conditions affecting the lungs is likely to find second-hand smoke can be a trigger. This is because the chemicals in tobacco smoke irritate the airways and the lungs and trigger asthma symptoms.
Parents need to be very aware that second-hand smoke can increase their child's risk of an asthma attack:
- Babies and children take more smoke into their lungs than adults. Because they're still growing and their immune system isn't fully developed yet, they're at greater risk from the toxins given out in the smoke.
- Babies and small children exposed to tobacco smoke are more likely to have respiratory infections and wheeze, and are more likely to go on to develop asthma as they get older.
- Older children diagnosed with asthma or being treated for asthma are at a high risk of smoke triggering asthma symptoms or an asthma attack.
Why is tobacco smoke a high risk trigger?
Smoke contains more than 4,000 chemicals, including carbon monoxide. Carbon monoxide makes it harder for oxygen to circulate round the body.
When you smoke, or breathe in smoke, you're taking the smoke right into your lungs. The chemicals in cigarette smoke irritate and inflame the airways and lungs. If you're a smoker, or regularly exposed to tobacco smoke, you'll have more symptoms and need more medicines to keep on top of your asthma. If your asthma symptoms get worse you're at risk of an asthma attack.
Even if you're not a smoker yourself, symptoms can come on quite quickly when you come into contact with someone else smoking.
"A few years back, I had a party and allowed people to smoke in my house. Two hours later I was in A&E because the cigarette smoke triggered a really bad asthma attack." - Michael Keenan
When am I most at risk?
You're most at risk of second-hand smoke triggering your asthma in small enclosed spaces such as bedrooms, living rooms and cars. This is because if people are smoking in a small place there'll be a very high concentration of toxic pollutants. Even opening a window won't make a significant difference. Tobacco smoke hangs around in the environment, and can stay in the room for several hours. If you smoke another cigarette in the room it tops up the pollutants already there. Smoke can stick to clothes and soft furnishings.
Cigarette smoke in a car is in very high concentrations. Smoking in cars is of particular risk to children because, as it's such an enclosed space, smoke can stay in the air for up to two and a half hours.
A new law, in force in England and Wales from 1 October 2015, makes it illegal to smoke in a car, or any vehicle, with anyone under 18 present. The law is designed to protect children and young people from the known dangers of second-hand smoke, one of which is to make asthma symptoms worse, increasing the risk of an asthma attack.
What about e-cigarettes and asthma?
E-cigarettes release doses of vaporised nicotine for the user to inhale.
While e-cigarettes are not risk-free, recent reviews of the evidence suggests that they are significantly less harmful than cigarettes in the short term - both for those who smoke them, and those who are around them. But very little research has been done so far looking at the effects on non-smokers with asthma exposed to e-cigarette vapours.
The new ban on smoking in cars with under 18s present doesn't apply to e-cigarettes. However, e-cigarettes have been banned from indoor use in other countries in Europe.
This is an issue where more evidence is emerging all the time. In the meantime, Asthma UK advises people with asthma to avoid inhaling anything into their lungs which may be harmful, as it could make their asthma worse. If you choose to use e-cigarettes (for example, as a way of giving up smoking), we recommend that you avoid using flavourings. At the moment there aren't many rules to control what substances are used, and there's a chance they could trigger an allergic reaction.
Shisha should be thought of as having the same risks as tobacco smoke. Shisha is linked to the same diseases. The same amount of smoke can be inhaled during a typical hour-long session as from more than 100 tobacco cigarettes. If you're around someone else smoking shisha there's a risk it will trigger asthma symptoms.
What's the best way to cut your risk of this trigger affecting you?
If you smoke, give up. Giving up smoking can be difficult, but it is one of the most important things that you can do to improve your asthma and your general health, and the health of your family. Once you are less exposed to cigarette smoke you'll really notice a difference - you'll have fewer asthma symptoms, be less breathless, and need to use fewer asthma medicines.
- If you live with a smoker, or have guests who smoke, ask them to smoke outside, well away from the door so the smoke doesn't drift into the house. Remember that even if people are smoking outside they'll be bringing particles in with them on their clothes.
- Keep your home smoke-free - for children in particular there's no safe level of exposure to second-hand smoke.
For advice, help and support to stop smoking:
Last updated July 2016
Next review due July 2019