Lung cancer in non-smokers is on the rise: What to know about second-hand and even third-hand smoke

On buses and MRT, in public spaces, and even at home, there’s always someone coughing. If that someone turns out to be you and you have been hacking away for weeks without signs of it going away, you might want to take note.
Along with other symptoms such as chest pain, wheezing, hoarseness as well as unexplained fatigue and weight loss, there might be a chance that you have lung cancer.
But wait, you’ve never been a smoker, so why should you be concerned? “Lung cancer is often perceived to be a smoker’s disease,” said Dr Toh Chee Keong, a medical oncologist with Curie Oncology. “It’s important that we establish that those who do not smoke can also be at risk.”
In fact, a 2018 study by National Cancer Centre Singapore showed that nearly half of lung cancer patients were never smokers. “This number represented an upward trend from a similar study conducted in 2006, indicating that there has been a rise in prevalence of lung cancer amongst non-smokers,” said Dr Toh.
Lung cancer is the third-most common cancer among males and females in Singapore. It is the leading cause of cancer death (25 per cent of all cancer-related deaths) among men, and the third-leading cause of cancer death (15 per cent) among women.
What’s also worrying is that lung cancer is often symptom-less (no coughing or any of the abovementioned signs) in the early stages, making it difficult to detect. Among the 8,955 men and women diagnosed with lung cancer between 2017 and 2021, 60 per cent were discovered to have Stage 4 cancer, according to the latest Singapore Cancer Registry Annual Report.
By then, the cancer could have spread to other parts and present as bone pain or tenderness, drooping eyelid, facial paralysis, shoulder pain and difficulty swallowing.
If you’re stifling a cough while reading this, here’s further information on why lung cancer can occur in non-smokers and what you can do to stay vigilant.
Fundamentally, your DNA goes into overdrive and churns out a lot more lung cells than needed very quickly. This results in a mass called a tumour, which can invade and destroy healthy lung tissues, according to Mayo Clinic.
Inhaling cigarette smoke exposes your lungs to many cancer-causing substances, noted the website. At first, your body is able to repair the damage. But with each repeated exposure, more healthy cells get damaged and causes them to change and eventually become cancerous.
There are generally two categories of lung cancer: Small cell lung cancer and non-small cell lung cancer.
The first group usually only includes heavy smokers who have smoked for years; the other category encompasses several types of lung cancer, including squamous cell carcinoma, adenocarcinoma and large cell carcinoma.
A family history certainly plays a part, particularly if you have a first-degree relative such as a parent, sibling or child who has lung cancer, said Dr Toh.
Interestingly, exposure to the fumes of cooking oil was found to be a strong risk factor as well, according to a two-year study involving 328 non-smoking women by Saw Swee Hock School of Public Health and the Duke-NUS Graduate Medical School.
It was discovered that those who cooked at home more than five times a week had higher levels of potential cancer-causing agents in their urine than those who didn’t cook.
One hypothesis is that the fumes created by intense stir-frying and deep-frying with a wok produce “vapours that contain a variety of potentially mutagenic and carcinogenic compounds”, said Professor Koh Woon Puay.
“Other factors,” said Dr Toh, “include exposure to gases such as naturally occurring radon, which is produced by the natural breakdown of uranium in soil, rock and water, which eventually becomes part of the air we breathe”.
There is evidence that living with a smoker can increase your risk of lung cancer from second-hand smoke exposure by 20 per cent to 30 per cent, according to this study.
“Tobacco smoke is made of a complex mixture of thousands of compounds,” said Dr Toh. “And the composition of second-hand smoke changes as it interacts with the environment.”
He continued: “Heavy smoking indoors can create extremely high PM levels, especially as second-hand smoke is able to linger in a room for up to about five hours – even travelling through stairwells and ventilation units”.
“Smoking tobacco forces tiny particles to be deposited deep in the bronchial tree and can lead to the development of cancer. The same may be true for vaping,” said Dr Stephen Broderick, a lung cancer surgeon at Johns Hopkins Medicine.
So don’t, for a moment, think that the second-hand emissions from e-cigarettes are just scented water vapours. Here’s what you’re inhaling, according to Johns Hopkins Medicine:
It refers to cigarette smoke’s residual nicotine and other harmful chemicals such as formaldehyde and naphthalene, said Dr Toh. “These substances can be found on indoor surfaces, skin, fur and furniture, even after the air has cleared.”
According to Mayo Clinic, third-hand smoke builds up on surfaces over time. “It can become embedded in most soft surfaces such as clothing, furniture, drapes, bedding and carpets. It also settles as dust-like particles on hard surfaces such as walls, floors and in vehicles.”

Not really because “cigarette smoke can linger in the house for hours, even with adequate ventilation”, said Dr Jonathan Tang, a consultant with National University Hospital’s Emergency Medicine Department.
“Leaning out of the window to puff does not prevent other household members from being exposed either,” he said. “Completely eliminating smoking is the only way to fully protect people who do not smoke from the harms of second-hand smoke exposure.”
Furthermore, third-hand smoke can remain for many months, even after smoking has stopped. People are exposed to the chemicals when they touch contaminated surfaces or breathe in the gases that third-hand smoke may release. “This poses a greater risk to children,” said Dr Tang, who are exposed more from crawling on the floor and putting objects in their mouths. 
Even after replacing the old carpet and giving the apartment a new coat of paint, studies suggest that third-hand smoke can still linger up to two months after smokers have vacated it, according to HealthHub. 
There is. It is known as a low-dose computerised tomography (LDCT) scan, and it takes a minute or less to perform.
Early and regular screening is encouraged for those who have a significant family history, or have been exposed to the abovementioned carcinogens frequently. “The treatment outcome improves significantly when lung cancer is diagnosed early,” said Dr Toh.
According to American Lung Association, your likelihood of surviving lung cancer five years or more improves to 63 per cent if the cancer is caught early.
You can get a free scan if you’re eligible for 365 Cancer Prevention Society’s current screening campaign called Are You At Risk?.