• Everyone with Crohn’s, Ulcerative Colitis or Microscopic Colitis is advised not to smoke.  
• Smoking increases your risk of developing Crohn’s. Smoking can also make Crohn’s worse. 
• You are less likely to develop Ulcerative Colitis if you smoke. If you already have Ulcerative Colitis, it is not clear whether smoking makes it better or worse.  
• Smoking increases your risk of developing Microscopic Colitis.  
• Cigarette smoke contains over 5,000 chemicals. Around 100 of these are known to be toxic or cause cancer.  
• Smoking can affect the choice of medicines available to you. Generally, Crohn's and Colitis medicines like filgotinib, tofacitinib and upadacitinib should not be given to people who smoke. 
• If you’re having surgery for Crohn’s or Colitis, your IBD team will recommend you stop smoking. This is to reduce the risk of complications. 
• It can be difficult to stop smoking. But you’re more likely to stop if you get support. The NHS offers local stop smoking services to help you stop successfully. 

The impact of smoking on Crohn’s 

Cigarette smoke contains over 5,000 chemicals. Around 100 of these are known to be toxic or cause cancer.  

Smoking in Crohn’s has been linked to: 

• More severe disease and complications. This includes strictures and perianal disease. A stricture is a narrowing in the bowel that can cause a dangerous blockage. Perianal disease is Crohn’s around your bottom. 
• More flare-ups. 
• Needing more treatment with steroids, immunosuppressants and anti-TNF medicines.  
• Needing your first surgery and then needing further surgery. 
• Crohn’s flaring-up again after surgery. 
• Developing complications outside of the gut. These include weak bones and joint problems.
• An increased risk of developing bowel cancer. 

Why smoking affects Crohn’s 

We do not know exactly what it is about smoking that affects Crohn’s. Not everyone who smokes will develop Crohn’s. And not everyone with Crohn’s will have smoked. 

Smoking could affect Crohn’s by: 

• Changing the bacteria that live in your gut.  
• Changing the way your genes work.  
• Changing your immune system. 
• Making the lining of your gut more leaky. This could make it easier for bacteria or other foreign substances to enter your blood and cause an immune response. 

The risk of developing Crohn’s if you smoke may be linked to your ethnic background. Smoking seems to increase the risk of developing Crohn’s if you are White. It does not seem to be as big a risk factor for Asian, Jewish and Latin American people. But more research is needed to know for sure. This includes more research on how Black people might be affected.

Should I stop smoking? 

Giving up smoking is important for people with Crohn’s. It’s never too late to quit. If you stop smoking, your risk factors return to that of someone who has never smoked, so that:  

• Your risk of a flare-up is the same as a non-smoker.  
• Your risk of needing surgery, or Crohn’s flaring-up again after surgery is the same as a non-smoker.  
• Your risk of getting complications outside the gut is the same as a non-smoker. 

The impact of smoking on Ulcerative Colitis

If you already have Ulcerative Colitis

It’s not clear how smoking affects Ulcerative Colitis in people who already have it.

Some studies find no difference between smokers and non-smokers with Ulcerative Colitis. This includes no difference in:

• The number of flare-ups or hospital admissions
• The need for steroids
• The need for surgery.

But other studies link smoking with Ulcerative Colitis to:

• Reduced gut inflammation and improved gut healing
• Fewer flare-ups and hospital admissions
• Less of a need for steroids

It can be confusing when different studies show different things. Many studies that show smoking might help Ulcerative Colitis are older. They also look at smaller groups of people. The studies that show smoking have no effect are newer and bigger but still have weaknesses and a risk of bias.  

All in all, at the moment we are not sure how smoking affects people’s Ulcerative Colitis.

Risk of colectomy

A colectomy is surgery to remove the colon. The risk of needing a colectomy is the same in smokers and non-smokers with Ulcerative Colitis.​ But compared to non-smokers, ex-smokers have a slightly bigger risk of needing a colectomy.

If you do not have Ulcerative Colitis

• Smoking makes you less likely to develop Ulcerative Colitis.
• Stopping smoking increases your risk of developing Ulcerative Colitis.

This appears to be the same for all ethnicities. But you should not start smoking to reduce your risk of developing Ulcerative Colitis. Smoking causes many serious health problems and is the biggest cause of early death in the UK.

Why smoking affects Ulcerative Colitis

We do not know exactly how or why smoking affects Ulcerative Colitis. Cigarette smoke contains over 5,000 chemicals. Around 100 of these are known to be toxic or cause cancer. Smoking could affect Ulcerative Colitis by:

• Changing the bacteria that live in your gut
• Changing the way your genes work
• Changing your immune system
• Increasing mucus production in your colon

The role of nicotine

Nicotine is an addictive chemical found in tobacco cigarettes. Some scientists think nicotine is the chemical in cigarettes that affects Ulcerative Colitis. Researchers cannot do a clinical trial to see if smoking helps Ulcerative Colitis. This is because of the harm cigarettes cause to the body. But as nicotine is not toxic, researchers have studied the effects of nicotine.

Some small studies showed a positive effect of nicotine on Ulcerative Colitis. But other studies found it was not an effective treatment and caused lots of side effects. At the moment, nicotine is not a routinely recommended treatment for Ulcerative Colitis.

Should I stop smoking?

Learning that smoking might have a positive effect on Ulcerative Colitis is confusing. It might make you unsure whether you should quit smoking. It’s important to remember the many other harmful effects of smoking. These include:

• Increased risk of cancer. In the UK, smoking is responsible for almost every 1 in 5 cancers.
• Increased risk of heart attacks.
• Increased risk of strokes.
• Increased risk of dementia.
• Increased risk of blood clots. People with Colitis are already at higher risk of developing blood clots.
• Complications in pregnancy. This includes miscarriage, still-birth and pre-term birth. People who smoke with Crohn’s or Ulcerative Colitis also have an increased risk of needing a Caesarian.
• Increased risk of developing weak bones, known as osteoporosis. This risk is already increased if you take steroids.

Cancer Research UK has produced a video about Brian and his experience of trying to stop smoking.

Managing flare-ups

You may be at risk of having a flare-up when you stop smoking. But there are lots of other health benefits to stopping smoking. Your IBD team will work with you to come up with a treatment plan before you stop smoking. This might include an increase in medication or closer monitoring. This way you can feel more confident in controlling your symptoms if needed.

Stopping smoking can be difficult. You’re more likely to stop if you get support. See the section on Getting help to stop smoking below.

Vapes, also called electronic cigarettes or e-cigarettes, can help people quit smoking. Vapes are not recommended for non-smokers.

Vapes are less harmful than smoking tobacco cigarettes. Some potentially harmful substances are produced by vapes, but these are in much lower levels than cigarettes. Tar and carbon monoxide are two of the most harmful substances in cigarettes. Vapes do not produce tar or carbon monoxide.

Although vaping is less harmful than smoking, it is not harm-free.

Early research shows vaping does not seem to make Crohn’s or Ulcerative Colitis worse. But much more research is needed to confirm this.

The NHS has more information on using vapes to stop smoking.

How smoking affects Microscopic Colitis

If you already have Microscopic Colitis

It’s not clear how smoking affects Microscopic Colitis in people who already have it. This is because there is not enough evidence. The available evidence suggests smoking does not affect symptoms. It may also not affect remission rates or the need for medicines.

If you do not have Microscopic Colitis

• Current smokers and ex-smokers have an increased risk of developing Microscopic Colitis.
• Smokers tend to develop Microscopic Colitis at a younger age than non-smokers or ex-smokers.

Should I stop smoking?

• Smoking increases the risk of complications after bowel surgery for Crohn’s or Colitis. This includes complications such as wound infections, pneumonia and sepsis.
• After surgery, you have a higher risk of developing blood clots in the legs or lungs. Smoking also increases the risk of developing blood clots. People with Crohn’s or Ulcerative Colitis are already at higher risk of developing blood clots.
• Smokers with Crohn’s are twice as likely to experience recurrence after surgery. Recurrence is when Crohn’s comes back, after previously being undetectable.
• If you are having surgery for Crohn’s or Colitis your IBD team will recommend you stop smoking.

Some research suggests smoking during pregnancy increases your child’s risk of developing Crohn’s or Ulcerative Colitis. But the evidence is not strong enough to say this for sure. Some research suggests a link to maternal smoking and developing Crohn’s. There is less research that suggests a similar link for Ulcerative Colitis.

Smoking or passive smoking during pregnancy carries other risks to you and your baby. See the NHS website for more on the benefits of stopping smoking during pregnancy

Some research suggests passive smoking increases the risk of developing Crohn's as a child. Other research finds no link between passive smoking in childhood and developing Crohn's or Ulcerative Colitis.

There is less research into the effect of childhood passive smoking on Ulcerative Colitis.

Teenagers and young people with Crohn’s or Colitis may experiment with smoking or vapes. Nearly 1 in 4 (25%) of all teenagers have tried vaping and 1 in 10 (10%) have tried smoking.

Young people’s lungs and brains are still developing. This means they are more sensitive to the effects of vaping.

The NHS has more information on young people and vaping. Frank also provides honest information for young people about vaping and nicotine.

Stopping smoking can be difficult. You might find it even harder to stop smoking if those around you smoke. But there are many advantages to quitting smoking:

• After 48 hours your lungs are clearing out mucus. Your senses of taste and smell are also improving.
• After 3 days breathing can feel easier, and your energy will increase.
• After 2 weeks blood will be pumping through to your heart and muscles much better.
• After 1 year, compared to a smoker, your risk of heart attack is halved.
• After 10 years your risk of dying from lung cancer is half that of someone who still smokes.

Some people tell us that they smoke to help with low mood, or fatigue. If you are trying to quit smoking, it might help to find other coping mechanisms. Our information on fatigue and mental health can help provide top tips.

Your IBD team, GP or other healthcare professionals can support you to stop smoking. Some pharmacists, private health insurers and employers also offer programmes to help you stop smoking.

If you have Ulcerative Colitis, you may be at risk of having a flare-up when you stop smoking. Your IBD team will work with you to come up with a treatment plan before you stop smoking.

Stop smoking treatments

Treatments available on the NHS are:

• Nicotine replacement therapy (NRT). This includes patches, chewing gum, lozenges, inhalers, nose and mouth sprays and tablets.
• A medicine called bupropion (Zyban).
• A medicine called varenicline.
• A medicine called cytisinicline.

Vapes can also help you stop smoking. But unlike NRT or medicines, vapes are not available on prescription from the NHS.

The NHS website has more information on stop smoking treatments, including:

• How to get stop smoking treatments
• Who they are suitable for
• Side effects of stop smoking treatments

Some people have told us they smoke cannabis to help with their Crohn’s or Colitis. This resource does not cover smoking cannabis. This is because medical cannabis cannot be prescribed for Inflammatory Bowel Disease on the NHS. Some private clinics might be able to prescribe cannabis treatments.

Use of cannabis from non-medical sources is illegal in the UK.

We follow strict processes to make sure our award-winning information is based on up-to-date evidence and is easy to understand. We produce it with patients, medical advisers and other professionals. It is not intended to replace advice from your own healthcare professional.

We hope that you’ve found this information helpful. Please email us at evidence@crohnsandcolitis.org.uk if:

• You have any comments or suggestions for improvements
• You would like more information about the evidence we use
• You would like details of any conflicts of interest

You can also write to us at Crohn’s & Colitis UK, 1 Bishop Square, Hatfield, AL10 9NE. Or you can contact us through our Helpline by calling 0300 222 5700.

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