How Smoking Cigarettes Affects Digestion

Your lungs aren't the only body parts that suffer from smoking

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As of Dec. 20, 2019, the new legal age limit is 21 years old for purchasing cigarettes, cigars, or any other tobacco products in the U.S.

Cigarette smoking affects all parts of the body, including the digestive system. This is especially damaging because the digestive system processes food into substances that are needed for the body to function properly.

In particular, people with Crohn's disease (one form of inflammatory bowel disease, or IBD) run the risk of their disease getting worse when they smoke.

Crohn's Disease

Smoking cigarettes has a negative effect on Crohn's disease. People who smoke, or who have smoked in the past, have been shown to have a higher risk of developing Crohn's disease than people who do not smoke.

People with Crohn's disease who smoke have an increased number of flare-ups, repeat surgeries, and a greater need for more aggressive treatment, such as immunosuppressants.

No one knows actually why smoking worsens the course of Crohn's disease. It is theorized that smoking may decrease blood flow to the intestines or that it could trigger a response in the immune system.

Even after quitting smoking, the former smoker still has an increased risk of developing Crohn's disease. However, there is an advantage for people with Crohn's disease who quit smoking. A year after quitting smoking, former smokers with Crohn's disease may experience a milder course of the disease.


Heartburn can also be caused by smoking. A valve at the end of the esophagus (the lower esophageal sphincter, or LES) normally keeps stomach acids from coming back up into the esophagus.

The LES is weakened by smoking, which results in stomach acid being able to enter the esophagus and cause heartburn. Smoking also seems to harm the esophagus directly, which hinders its ability to resist damage.

Additionally, smoking interferes with the movement of bile salts. Bile salts move from the intestine to the stomach. When this does not occur (a disease called duodenogastric reflux) the stomach acid becomes more acidic and can further damage the esophagus.

Liver Disease

Another organ in the digestive tract that is adversely affected by smoking is the liver. The liver is an important organ which filters toxins from the body. These toxins include medications and alcoholic beverages.

The function of the liver may be hindered by cigarette smoke. When this happens, a different dose of medication is needed to achieve the desired effect on an illness or disease. Smoking can also aggravate existing liver disease caused by alcoholism.

People with IBD are also at an increased risk for certain liver diseases, such as primary sclerosing cholangitis (which is found primarily in those with ulcerative colitis), autoimmune hepatitis, and primary biliary cirrhosis.

The potential risk of liver disease is one more reason that people with IBD should not smoke cigarettes.

Peptic Ulcer

Smokers have a higher chance of developing an ulcer (a hole in the stomach). If a smoker gets an ulcer, it typically takes longer to heal and has a greater chance of being fatal than it is in nonsmokers. No one is certain about why this is so, but it could be due to the variety of effects smoking has on the digestive tract.

Smoking decreases the amount of sodium bicarbonate produced by the pancreas. Without it, stomach acid is not neutralized in the duodenum (first part of the small intestine).

This could contribute to ulcers forming in the duodenum. Also, smoking may cause an increase in the amount of stomach acid that is flowing into the small intestine.

A Word From Verywell

Smoking causes serious and sometimes irreversible damage to the digestive tract. It's estimated that 400,000 people die each year as a result of smoking cigarettes. These deaths, and the suffering that precedes them, are completely preventable with smoking cessation programs.

IBD and smoking have an intimate relationship, and people with Crohn's disease especially should quit smoking in order to prevent their disease from becoming more serious and causing further complications.

Conversely, some people who didn't have any digestive problems while they smoked develop ulcerative colitis after they stop smoking. Ulcerative colitis is sometimes called a disease of non-smokers. But that doesn't mean it's safe to start smoking again to try to treat the disease.

The harms to health caused by smoking are always going to outweigh any perceived benefits. No one should smoke, but people with IBD should be especially aware of the digestive problems smoking will cause and consult a doctor about a smoking cessation program.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Johnson GJ, Cosnes J, Mansfield JC. Review article: Smoking cessation as primary therapy to modify the course of Crohn's disease. Aliment Pharmacol Ther. 2005;21(8):921-31.

  2. The National Digestive Diseases Information Clearinghouse. Smoking and your digestive system. National Institute of Diabetes and Digestive and Kidney Diseases. 14 Sept 2013.

  3. Yamamoto T. Factors affecting recurrence after surgery for Crohn's disease. World J Gastroenterol. 2005;11:3971-3979. 

Additional Reading

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.