Overview
Irritable Bowel Syndrome (IBS) and Lactose Intolerance both cause digestive discomfort, but their causes and symptom patterns differ. IBS is a functional gastrointestinal disorder affecting how the gut works, often triggered by stress, diet, or hormones. Lactose intolerance is a food intolerance caused by the inability to digest lactose, a sugar found in dairy. While both may lead to bloating, gas, and diarrhea, IBS symptoms are more chronic and varied, whereas lactose intolerance occurs specifically after consuming dairy.
Disease Summaries
IBS: Irritable Bowel Syndrome (IBS) is a condition with recurring episodes of abdominal discomfort, diarrhea, and constipation. IBS is diagnosed when no clear cause can be found despite investigations. The exact cause of IBS is unknown, but stress and certain foods are known to cause flare-ups.
Lactose Intolerance: Lactose Intolerance is a condition in which milk is poorly digested and absorbed. This occurs more commonly in adults, as the enzyme for digesting milk (lactase) decreases with age. Other risk factors include recent gut infections and non-Caucasian ethnicity.
Comparing Symptoms
Overlapping Symptoms
- Abdominal bloating
- Gas or flatulence
- Diarrhea
IBS Specific Symptoms
- Alternating constipation and diarrhea
- Abdominal pain relieved by bowel movement
- Mucus in stool
- Symptoms often triggered by stress or specific foods
- Chronic and recurring symptoms
Lactose Intolerance Specific Symptoms
- Diarrhea shortly after consuming dairy
- Nausea or stomach rumbling after dairy intake
- No symptoms when avoiding lactose
- Symptoms begin within a few hours of eating dairy
Treatment Approaches
IBS Treatment Approaches
Treatment involves dietary modifications to identify and avoid trigger foods, stress management techniques, and medications to control specific symptoms like diarrhea or constipation. Probiotics and fiber supplements may be helpful for some patients. Psychological support through cognitive behavioral therapy can help manage stress-related symptoms.
Lactose Intolerance Treatment Approaches
Reducing milk consumption can alleviate symptoms. Other options include switching to lactose-free milk, non-dairy milk, or taking lactase supplements before consuming dairy products.
Reviewed By:

Kenji Taylor, MD, MSc (Family Medicine, Primary Care)
Dr. Taylor is a Japanese-African American physician who grew up and was educated in the United States but spent a considerable amount of time in Japan as a college student, working professional and now father of three. After graduating from Brown, he worked in finance first before attending medical school at Penn. He then completed a fellowship with the Centers for Disease Control before going on to specialize in Family and Community Medicine at the University of California, San Francisco (UCSF) where he was also a chief resident. After a faculty position at Stanford, he moved with his family to Japan where he continues to see families on a military base outside of Tokyo, teach Japanese residents and serve remotely as a medical director for Roots Community Health Center. He also enjoys editing and writing podcast summaries for Hippo Education.

Aiko Yoshioka, MD (Gastroenterology)
Dr. Yoshioka graduated from the Niigata University School of Medicine. He worked as a gastroenterologist at Saiseikai Niigata Hospital and Niigata University Medical & Dental Hospital before serving as the Deputy Chief of Gastroenterology at Tsubame Rosai Hospital and Nagaoka Red Cross Hospital. Dr. Yoshioka joined Saitama Saiseikai Kawaguchi General Hospital as Chief of Gastroenterology in April 2018.
Content updated on Apr 29, 2025
Following the Medical Content Editorial Policy
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Link to full study:
https://www.medrxiv.org/content/10.1101/2024.08.29.24312810v1References
Di Costanzo M, Berni Canani R. Lactose Intolerance: Common Misunderstandings. Ann Nutr Metab. 2018;73 Suppl 4:30-37. doi: 10.1159/000493669. Epub 2019 Feb 19. PMID: 30783042.
https://www.karger.com/Article/FullText/493669Szilagyi A, Ishayek N. Lactose Intolerance, Dairy Avoidance, and Treatment Options. Nutrients. 2018 Dec 15;10(12):1994. doi: 10.3390/nu10121994. PMID: 30558337; PMCID: PMC6316316.
https://www.mdpi.com/2072-6643/10/12/1994Borghini R, Donato G, Alvaro D, Picarelli A. New insights in IBS-like disorders: Pandora's box has been opened; a review. Gastroenterol Hepatol Bed Bench. 2017 Spring;10(2):79-89. PMID: 28702130; PMCID: PMC5495893.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5495893/