Heartburn happens when stomach acid flows backward into your esophagus, the tube connecting your mouth to your stomach. At the bottom of that tube sits a ring of muscle that normally opens to let food pass into your stomach, then closes to keep acid where it belongs. When that muscle weakens or relaxes at the wrong time, acid escapes upward and burns the sensitive lining of your esophagus. What’s causing yours depends on a mix of anatomy, habits, and sometimes medications or medical conditions.
How the Valve at Your Stomach Fails
That ring of muscle, called the lower esophageal sphincter, is the gatekeeper. Two patterns of dysfunction cause most heartburn: the muscle relaxes too frequently when it shouldn’t, or its resting pressure is too low to hold acid back in the first place. Both problems stem primarily from faulty nerve signaling to the muscle rather than damage to the muscle itself. This is why heartburn can come and go. Your sphincter may work fine most of the time but fail under certain conditions, like after a large meal, when you’re stressed, or when something you ate or drank weakened its tone.
Foods and Drinks That Trigger Reflux
Not all food triggers work the same way. Some relax that sphincter muscle directly, while others irritate your esophagus on the way down.
Chocolate contains both caffeine and cacao, both of which relax the sphincter and make it easier for acid to escape. Coffee does the same thing through its caffeine content, and it also stimulates your stomach to produce more acid, a double hit. Citrus fruits and tomatoes don’t weaken the sphincter at all. Instead, their naturally acidic pH irritates esophageal tissue that may already be inflamed from earlier reflux episodes. Spicy foods, fatty meals, and peppermint are other common culprits.
This distinction matters because it changes what you can experiment with. If chocolate and coffee consistently trigger your symptoms, your sphincter is probably the weak link. If acidic foods are the main problem, your esophagus may already be irritated, and reducing overall reflux (not just avoiding citrus) will help more.
Smoking and Alcohol Lower Your Defenses
Both tobacco and alcohol reduce the resting pressure of the sphincter muscle, making reflux physically easier. This isn’t a temporary effect tied to a single cigarette or glass of wine. Regular use keeps sphincter pressure chronically lower than it should be. If you smoke and drink and also eat late at night, you’re stacking three separate mechanisms that all push acid in the wrong direction.
When You Eat Matters as Much as What You Eat
Gravity is one of your best defenses against reflux. When you’re upright, acid has to travel uphill to reach your esophagus. When you lie down, the playing field levels out and acid flows freely. Eating a big dinner and going to bed an hour later is one of the most reliable ways to trigger nighttime heartburn.
The general guideline is to wait at least three hours after eating before lying down. That gives your stomach enough time to empty most of its contents and reduces the volume of acid available to reflux. If nighttime heartburn is your main problem, elevating the head of your bed by six inches (using blocks under the bedframe, not just extra pillows) can also help by keeping gravity on your side while you sleep.
Excess Weight Puts Physical Pressure on Your Stomach
Carrying extra weight around your midsection increases the pressure inside your abdomen, and that pressure pushes against your stomach from the outside. Research has shown that waist circumference and abdominal depth correlate strongly with intra-abdominal pressure. Even a normally functioning sphincter can be overwhelmed when there’s enough force pushing stomach contents upward.
This is why heartburn often worsens with weight gain and improves with weight loss. Studies on patients who lost significant weight through surgery found measurable drops in abdominal pressure and corresponding decreases in reflux symptoms. You don’t need surgery to see benefits. Losing even a moderate amount of abdominal fat can reduce the mechanical pressure driving your reflux.
Pregnancy and Hormonal Changes
If you’re pregnant, heartburn is almost expected. Progesterone levels rise steadily throughout pregnancy, and this hormone relaxes smooth muscle tissue throughout your body, including the sphincter at the top of your stomach. Research shows that sphincter pressure drops progressively during pregnancy, reaching its lowest point around 36 weeks. Combine that weakened sphincter with a growing uterus pushing your stomach upward, and reflux becomes nearly unavoidable in the third trimester. The good news is that it typically resolves after delivery once hormone levels normalize and the physical pressure disappears.
A Hiatal Hernia Can Change Your Anatomy
Your esophagus passes through a small opening in your diaphragm before connecting to your stomach. In a hiatal hernia, the upper portion of your stomach pushes through that opening and slides into your chest cavity. A small hernia may cause no symptoms at all, and many people have one without knowing it. But a larger hernia traps a portion of your stomach above the diaphragm, which disrupts the sphincter’s ability to close properly and allows acid to back up into the esophagus more easily. Hiatal hernias are more common as you age and in people who are overweight. If your heartburn is persistent despite lifestyle changes, this is one of the structural causes your doctor may investigate.
Medications That Cause or Worsen Heartburn
Several common medications can trigger heartburn as a side effect. Anti-inflammatory painkillers like ibuprofen and naproxen irritate the stomach lining and can increase acid production. Bisphosphonates, which are widely prescribed for osteoporosis, are another frequent offender. Roughly one in four women starting bisphosphonate therapy experienced gastrointestinal problems, including reflux, within the first year. For women who already had digestive issues before starting the medication, that rate climbed above 50%.
Other medications that can contribute include certain blood pressure drugs, sedatives, and some antidepressants. If your heartburn started or worsened around the time you began a new medication, that timing is worth noting and discussing with whoever prescribed it.
Symptoms That Signal Something More Serious
Most heartburn is uncomfortable but not dangerous. However, certain symptoms alongside heartburn point to complications that need prompt evaluation:
- Trouble swallowing or a sensation of food getting stuck, which can indicate narrowing of the esophagus
- Unintentional weight loss without a clear explanation
- Vomiting blood or material that looks like coffee grounds
- Black or red stools, which suggest bleeding somewhere in the digestive tract
- Chest pain during physical activity like climbing stairs, which may not be heartburn at all
These are considered alarm symptoms by the American Gastroenterological Association and warrant a conversation with a healthcare provider rather than continued self-treatment with antacids.
Narrowing Down Your Personal Triggers
Heartburn rarely has a single cause. For most people, it’s a combination of a sphincter that doesn’t seal perfectly, dietary habits that weaken it further, and timing or positional factors that give acid an easy path upward. The most practical approach is to track your episodes for a week or two. Note what you ate, when you ate it, what position you were in when symptoms hit, and how severe the burn was. Patterns tend to emerge quickly. You may discover that it’s not coffee in general but coffee on an empty stomach, or not dinner itself but dinner followed by lying on the couch. Those specifics let you make targeted changes instead of eliminating everything at once.