However, we don’t yet fully understand what causes Crohn’s. Not everyone who smokes will develop Crohn’s. And not everyone with Crohn’s will have smoked.

The risk of developing Crohn’s if you smoke may be linked to your ethnic background. But more research is needed to understand this link.

Smoking in Crohn’s has been linked to:

• More severe disease and complications. These include 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 (anus).
• 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, such as weak bones and joint problems. These are also called extraintestinal manifestations (EIMs).
• An increased risk of developing bowel cancer.

How does smoking affect Crohn’s?

We don’t know exactly what it is about smoking that affects Crohn’s. Cigarette smoke contains over 5,000 chemicals. Around 100 of these are known to be toxic or cause cancer. 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 pass into your blood and trigger an immune response.

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 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.

Even reducing how much you smoke may help with your Crohn’s. People who smoke less have fewer complications outside the gut. They also have a lower risk of strictures than heavy smokers.

It’s not clear whether smoking changes Ulcerative Colitis. Some studies show that smokers have a milder form of Ulcerative Colitis. This includes fewer flare-ups, hospital admissions, and less need for steroids or immunosuppressants. But other studies find no difference between smokers and non-smokers with Ulcerative Colitis.

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. Ex-smokers with Ulcerative Colitis have a small increased risk of needing a colectomy compared to non-smokers.

How does smoking affect Ulcerative Colitis?

We don’t know exactly what it is about smoking that 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.

Nicotine replacement therapy for Ulcerative Colitis

Researchers can’t do a clinical trial to see if smoking helps Ulcerative Colitis because of the harm cigarettes cause to the body. However nicotine is not toxic, so some studies have looked at the effects of nicotine replacement therapies (NRT) on Ulcerative Colitis. Studies on the impact of nicotine on Ulcerative Colitis have used nicotine patches, nicotine chewing gum or nicotine enemas.

NRT was more effective than the placebo (a dummy treatment with no nicotine) in getting people with Ulcerative Colitis into remission. NRT was as effective, but not better than standard medicines, such as aminosalicylates (5-ASAs) or steroids, in getting people with Ulcerative Colitis into remission.

Unwanted side effects were common with NRT. Some people stopped their treatment with NRT early because of unwanted side effects.

Talk to your IBD team if you’re thinking about trying NRT.

Should I stop smoking?

It might be tempting to continue or even take up smoking to try to help your Ulcerative Colitis. But it’s important to remember the many other harmful effects of smoking. Smoking is one of the biggest causes of illness and death in the UK.

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. This way you can feel more confident in controlling your symptoms if your Colitis is affected by stopping smoking.

Passive smoking in babies and children

Passive smoking is breathing in someone else’s cigarette smoke. It’s also known as second-hand smoke.

It’s not clear if passive smoking while you’re in the womb or as a child affects your risk of developing Crohn’s Disease or Ulcerative Colitis. Some research suggests your risk of Crohn’s or Colitis is increased if you were exposed to cigarette smoke in the womb or as a child. But newer research has not found any increased risks from passive smoking in the womb or as a child.

Passive smoking in adults

Some studies have looked at passive smoking in adults with Crohn’s who have never smoked. In one study, adults exposed to passive smoking needed more medicines than those who had not been exposed to passive smoking. These medicines included immunosuppressants and infliximab. In another study, adults exposed to passive smoking were more likely to need surgery for their Crohn’s than people who were not exposed to passive smoking.

Passive smoking does not affect the need for medicines, hospital admissions or surgery in adults with Ulcerative Colitis who have never smoked.

Compared with people who have never smoked, current smokers and ex-smokers have an increased risk of developing:

• Collagenous Colitis
• Lymphocytic Colitis

Smokers tend to develop Microscopic Colitis at an earlier age than non-smokers or ex-smokers. Most studies show that smoking does not affect symptoms, remission rates or the need for medicines in Microscopic Colitis.

More research is needed to know if stopping smoking can help Microscopic Colitis. But it’s important to remember the many other harmful effects of smoking.

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.

Stopping smoking can be difficult. You might find it even harder to stop smoking if those around you smoke.

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

Stop smoking treatments available on the NHS are:

• Nicotine replacement therapy (NRT), such as patches, chewing gum, lozenges or inhalers.
• A medicine called bupropion (Zyban).

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

Electronic cigarettes are also known as e-cigarettes or vapes. E-cigarettes allow you to inhale nicotine without smoking a cigarette. E-cigarettes are much less harmful than smoking tobacco cigarettes. Some potentially harmful substances are produced by e-cigarettes, but these are in much lower levels than cigarettes. Tar and carbon monoxide are two of the most harmful substances in cigarettes. E-cigarettes do not produce tar or carbon monoxide.

Not much is known about the impact of e-cigarettes on Crohn’s and Colitis. Smoking e-cigarettes does not seem to make Crohn’s or Colitis worse. But much more research is needed to confirm this.

E-cigarettes with nicotine are effective in helping people to quit smoking. They are more effective than other types of nicotine replacement therapy (NRT). Unlike NRT, e-cigarettes are not available on prescription from the NHS. The NHS has more information on using e-cigarettes to stop smoking.

We follow strict processes to make sure our information is based on up-to-date evidence and easy to understand.

Please email us at evidence@crohnsandcolitis.org.uk if:

• You have any comments or suggestions for improvements
• You would like more information about the sources of 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 contact us through our Helpline: 0300 222 5700