While inflammatory bowel disease (IBD) can occur at any age, research shows that it tends to onset between ages 15 to 29. However, late- or early-onset IBD can still occur in those outside of this age group.

IBD refers to a group of intestinal disorders that include ulcerative colitis (UC) and Crohn’s disease. The condition is chronic and is characterized by ongoing inflammation in the digestive tract.

Although scientists think the condition is likely genetic, it also appears to be strongly influenced by environmental and lifestyle factors. The disease may be triggered by factors like family history, smoking, early-life exposure to antibiotics, and a sedentary lifestyle.

Medical experts believe the condition’s onset to be dependent on several factors, but further research is still needed. Here’s what to know about the onset of IBD.

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According to the Centers for Disease Control and Prevention (CDC), IBD is most frequently diagnosed in people between ages 15 to 29, a time commonly referred to as young or emerging adulthood.

In a 2020 study, a small sample of emerging adults with IBD had an average age of around 25 and had the condition for an average of 6.4 years. That being said, researchers noted that most studies on the condition are conducted on adults ages 40 to 50, which means that early symptoms of IBD are currently under-researched.

Among emerging adults, the most common symptoms include:

  • fatigue
  • abdominal cramps
  • abdominal pain
  • diarrhea

Fatigue was the most commonly reported complaint among young adults with IBD.

Only about 10% of people are diagnosed before they turn 18.

In part because the disease onsets in early adulthood, scientists believe that there’s a strong argument for IBD being influenced by both genetic and environmental risk factors — more on that below.

Even though the exact causes of IBD remain unknown, research suggests that certain environmental factors may trigger or worsen the condition.

According to a 2022 review of several studies, these include:

  • prenatal exposure to antibiotics in the first year of life
  • early-life otitis media (which may be treated with antibiotics)
  • smoking or second-hand smoke
  • higher intake of ultra-processed food
  • vitamin D deficiency

Air pollution and a sedentary lifestyle may also play a role.

This suggests in part that eliminating excess bacteria from the gut (via antibiotic use), and environment (via sanitization) in early life may actually increase the odds of developing IBD down the road. Scientists theorize that this could influence the onset of the condition, especially when combined with an irregular gut environment.

There’s also a particularly notable spike in diagnoses of IBD in countries that are newly industrialized, which could be in part due to this relationship. Those in industrialized countries may also be more likely to consume ultra-processed food.

Other risk factors for IBD include:

  • Family history: If your parent, sibling, or child has IBD, you’re also more likely to have it. For that reason, scientists believe the condition has a strong genetic link.
  • Ethnicity: Though IBD is present across populations, white people are much more likely to have it.
  • Your immune system: The immune system appears to play a crucial role in the development of IBD. Those with IBD appear to have an exaggerated immune response to bacteria and/or viruses, causing the digestive tract to remain inflamed and attack itself even when there’s no serious threat present.
  • Comorbid conditions: You’re more likely to get IBD if you have certain pre-existing conditions, including other immune-linked diseases like asthma, arthritis, psoriasis, and multiple sclerosis.

First-line treatment for IBD currently typically involves anti-inflammatory drug therapy, including:

  • corticosteroids, such as budesonide, prednisone, and methylprednisolone
  • aminosalicylates, such asbalsalazide, mesalamine, and sulfasalazine
  • immunomodulators, such as methotrexate, azathioprine, and mercaptopurine
  • biologics, such as certolizumab, ustekinumab, and vedolizumab

Other medications include:

  • antibiotics, such as metronidazole and ciprofloxacin
  • antidiarrheal medications

Surgery is considered an option in more severe cases. It may include widening sections of narrowed bowels, closing or removing fistulas, or removing parts of the intestines. In severe cases, it may involve removing the entire colon and rectum.

Lifestyle changes and supplements may also help prevent and treat IBD, including:

  • tracking and avoiding individual dietary triggers
  • reducing stress
  • drinking lots of fluids
  • drinking less alcohol
  • quitting smoking, if you smoke
  • eating less sugar
  • eating less processed food
  • moving your body regularly
  • taking vitamin or mineral supplements

Can IBD develop suddenly?

It is possible for IBD to develop suddenly. While the exact cause of IBD is unknown, research suggests that environmental factors such as prenatal exposure to antibiotics, smoking, and vitamin deficiencies can lead to the onset of IBD.

Can IBD start at any age?

While IBD can start at any age, it’s most likely to occur between the ages of 15 and 29.

What are the early signs of Crohn’s disease?

Early signs of Crohn’s disease can include fatigue, diarrhea, abdominal pain, and blood in stool. Consider speaking with a doctor if you think you may be experiencing Crohn’s symptoms.

IBD typically onsets between ages 15 to 29 and may be influenced by a combination of genetic and lifestyle factors. Fatigue is the most commonly reported complaint in this age group, followed by abdominal pain.

Smoking, early-life antibiotic use, air pollution, and a sedentary lifestyle are all linked to its onset. IBD can be treated with anti-inflammatory therapy, healthy lifestyle changes, and in some cases, surgery.