1. Can stomach pain with no cause found by doctors be just "in your head"?
Sometimes, medical tests show no injury or disease in the stomach or intestines, yet the pain continues. Doctors call this functional abdominal pain. At Seattle Children’s Hospital, they say this applies to about 90% of children with long-lasting stomach pain [5]. The proportion of school-age children affected varies widely depending on the study, ranging from 0.3% to 19% in US and European data, though these numbers do not apply to Japan [5].
So, is this pain just imaginary? Doctors say no. The pain is actually felt, and it is linked to communication between the brain and the gut. The brain and digestive tract are connected by the autonomic nervous system, hormones, and cytokines (chemical messengers sent by cells). Information travels both ways: from the brain to the gut, and from the gut to the brain. This two-way communication is called the "brain-gut axis" [1].
Harvard Medical School explains that emotions like anxiety, anger, or sadness can affect the gut. A struggling gut can send signals to the brain, and a struggling brain can send signals to the gut [2]. In English, people sometimes call the nervous feeling in the stomach "butterflies."
2. How does the brain's stress hormone CRF affect the large intestine?
When the brain feels worried, what happens inside the body? One clue is a hormone called CRF (corticotropin-releasing factor). Stress causes the hypothalamus in the brain to release more CRF. According to a review in the Journal of the Medical Association of Nippon Medical School, CRF acting on the large intestine lowers the threshold for pain, making nerves more sensitive [1]. It also increases the movement of the intestinal wall and the permeability of the lining, which can cause diarrhea [1]. This means the gut becomes more sensitive to pain and moves more at the same time.
However, the paper states that CRF is "suggested to be involved." It is not certain that CRF alone explains everything. This is part of ongoing research into the mechanisms of irritable bowel syndrome (IBS), which is discussed later.
3. How does stress change gut movement and turn it into stomach pain?
There are at least two reasons why the stomach hurts. Materials from a study group at Nagasaki University on pediatric psychosomatic medicine explain that stress and the fear of symptoms returning can trigger abnormal gut movement and hypersensitivity in the gut. These signals travel from the brain’s cerebrum, hypothalamus, and amygdala via CRF [3]. Spasms in the gut are felt as pain. When gut sensation becomes sensitive, the same movement feels more painful [3].
The appearance of the stool changes depending on how the gut moves. Fast movement causes diarrhea, while slow movement causes hard, pellet-like stools [3]. Note that this Nagasaki material was modified in 2006 for study purposes, so it is used alongside newer academic reviews.
Doctors at Seattle Children’s Hospital use the metaphor of "volume" to explain pain sensitivity. Stress turns up the volume at which the brain receives pain signals [5]. Movements in the gut that are usually ignored become loud and noticeable. This is just a metaphor; there is no actual dial in the brain.
4. How can worry about pain create a negative cycle and IBS?
When pain lasts a long time, worry about it coming back can start a cycle. The review from Nippon Medical School states that stress-induced pain intensification leads to more anxiety. This anxiety becomes psychological stress that affects the digestive tract, creating a "negative chain" [1].
One condition where this cycle lasts a long time is irritable bowel syndrome (IBS). It is a group of symptoms involving repeated stomach pain and changes in bowel habits. It is a common cause of stomach pain in children and is known to be closely related to stress, though the exact cause is not known [1].
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in the US says there are no visible injuries in the intestines of people with IBS. They list "problems with the brain-gut connection" as a possible cause, noting that the gut may become more sensitive to pain and bloating [4]. In the US, about 12% of people fit this description, but this is not the rate for children or people in Japan [4]. It is important not to assume every child with stomach pain has IBS. IBS is a medical diagnosis made by a doctor.
5. What do we know and not know about the nerves in the gut wall?
Inside the gut wall is a network of nerves called the enteric nervous system. It is said to control gut movements without needing the brain or spinal cord. There are a few hundred million nerve cells here, but the exact number varies by source, so treat this as an estimate [7].
Research is slowly revealing the path from brain to gut. A study by Gifu University and others published in 2026 showed that psychological stress (avoiding water) in rats caused defecation. A path from the hypothalamus to the medulla, then the spinal cord’s defecation center, and finally the pelvic nerves was activated, increasing large intestine movement. Blocking this path reduced stress-induced defecation [6]. However, this was an acute stress test in rats, and it is not yet known if it works the same way in humans.
We know the vagus nerve and spinal nerves carry signals from the gut to the brain. But the specific factors and circuits involved are not well understood [1]. Recently, scientists found that gut bacteria are also involved in the brain-gut axis. Abnormal bacterial growth in the small intestine has been reported in patients with IBS, among other findings [1][8]. Questions about why symptoms differ from person to person are still being researched.
6. How can recording your stomach signals help you understand them?
Knowing that stomach pain is not "just in your head" can change how you see it. You might try recording your body’s signals so you can read them later. On a day when your stomach hurts, write one line: the time, place, what you were doing, how you felt, and what you ate. After a few days, you might see patterns, like "it happens the day before a presentation" or "it happens in the morning." This is not to find a disease, but to help you talk to a doctor.
If pain continues, do not endure it. Talk to your parents or a doctor. SAFETY NOTE: If pain continues, do not just keep records; talk to a guardian or doctor.
Some of the Japanese sources listed have many diagrams and are easy to read. Comparing the Nippon Medical School review and the Nagasaki University study materials to find similarities and differences is a recommended way to learn.