Merck Manuals Details What Patients Need to Know About Inflammatory Bowel Disease

RAHWAY, N.J., Sept. 23, 2026 /PRNewswire/ -- When patients experience prolonged diarrhea and abdominal pain, one condition doctors may consider is inflammatory bowel disease (IBD). In IBD, different parts of the gastrointestinal tract become inflamed, often causing recurring abdominal pain and diarrhea. If left untreated, the inflammation from IBD can lead to serious complications.

In a new editorial from MerckManuals.com, Aaron E. Walfish, MD, Mount Sinai Medical Center, shares key information on IBD, including recent advances in treatment options.

IBD is different from IBS

IBD is sometimes confused with irritable bowel syndrome (IBS). The two have similar acronyms and some similar symptoms, but they are fundamentally different conditions, says Walfish. IBS is a functional disorder, meaning the digestive tract can appear normal but does not function properly.

IBD, on the other hand, involves chronic inflammation that can be detected during a colonoscopy or through imaging and confirmed through biopsies. Untreated IBD can cause permanent damage and complications including fistulas, which are abnormal tunnels forming between parts of the gastrointestinal tract, other organs, or the skin, and abscesses, which are pus-filled cavities, undernutrition, and an increased risk of colorectal cancer. And because IBD is a systemic inflammatory disease, it may also cause inflammation and symptoms in other parts of the body, including joint pain or joint inflammation, eye inflammation, skin conditions, and fatigue.

Crohn disease and ulcerative colitis are the two primary types of IBD

Most people with IBD have either Crohn disease or ulcerative colitis, says Walfish.

Crohn disease is marked by chronic inflammation typically affecting the lower part of the small intestine, the large intestine, or both. However, inflammation may affect any part of the digestive tract.

In ulcerative colitis, the large intestine (colon) often becomes inflamed and ulcerated (pitted or eroded), often leading to bouts of bloody diarrhea, abdominal cramps, and fever.

There is no cure for IBD

Doctors don't fully understand what causes IBD, says Walfish. Evidence suggests normal intestinal bacteria inappropriately trigger an immune reaction in people with a genetic predisposition. Several additional risk factors have also been identified, including smoking.

While there is no cure for IBD, treatments have advanced considerably in recent decades. Treatment approaches generally focus on controlling inflammation and healing the lining of the gastrointestinal tract, both of which can help prevent complications and improve quality of life for patients.

IBD needs to be treated – regardless of symptoms

When IBD is more active, it's known as a "flare-up," and patients experience more symptoms. Periods without symptoms are known as remission.

Sometimes, patients with IBD think that if they are not experiencing symptoms, they are better and don't need to continue treatment. This is not true, says Walfish. Even when symptoms are not occurring, patients can still have inflammation, leading to further damage and complications. Adhering to treatment, including medications and regular monitoring and appointments, is essential.

Diet and stress do not cause IBD

Eating certain foods or avoiding others cannot cure IBD, says Walfish. Still, nutrition can play an important role in symptom management and overall health. People with IBD should eat healthy, balanced meals and stay hydrated, particularly after a flare-up.

Similarly, while stress does not cause IBD, it can lead to flare-ups and make symptoms worse during a flare-up, says Walfish.

Ultimately, managing IBD includes staying current on preventive care and treatment, focusing on good sleep, controlling stress, staying active, and building a strong relationship with a treating physician.

To read more of Walfish's insights on IBD, visit the editorial at MerckManuals.com.

About The Merck Manuals and MSD Manuals

First published in 1899 as a pocket-sized reference for physicians and pharmacists, The Merck Manual has evolved into one of the world's most trusted and widely-used medical resources. Today, it serves professionals and consumers alike with expert-authored, regularly updated medical content. Available in 16 languages and reaching nearly 250 countries, The Manuals offer far more than text. The website and mobile apps feature an ever-growing collection of videos, podcasts, infographics, and interactive 3D models designed for medical professionals, students, veterinarians, and curious consumers. For over a century, The Merck Manual has been fully committed to making reliable medical knowledge accessible to everyone, everywhere. Access The Manuals online in the United States and Canada at MerckManuals.com, and worldwide at MSDManuals.com. 

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

SOURCE The Merck Manuals