Hiccups are an involuntary reflex caused by sudden spasms of the diaphragm, the muscle that separates the chest and abdominal cavities. The glottis---a tissue flap that protects the airway during swallowing---snaps shut as the diaphragm spasms, causing the characteristic noise associated with a hiccup. While hiccups are annoying, they are rarely a cause for concern unless they persist. Most causes of hiccups relate to transient stimulation of one of the nerves of the chest.
Stomach Bloating
Stomach bloating may trigger a brief episode of hiccups, according to Dr. Robert Shmerling of Beth Israel Deaconess Medical Center in an article on hiccups published on InteliHealth.com. Possible causes of stomach bloating include overeating, drinking excessive amounts of fluids, drinking carbonated beverages, swallowing excessive air and smoking. Eating or drinking extremely hot, cold or spicy foods may also provoke a bout of hiccups.
Abdominal Disorders
According to the National Health Service of the United Kingdom, abdominal diseases and disorders can trigger a prolonged bout of hiccups. Disorders that may stimulate hiccups include chronic stomach inflammation, or gastritis; anorexia nervosa; blockage of the small intestine; appendicitis; peptic ulcer disease; Crohn's disease; gallbladder inflammation, or cholecystitis; and abdominal surgery.
Alcohol Consumption and Emotional Extremes
Although the mechanism remains unclear, consumption of excessive alcohol can cause hiccups, notes MayoClinic.com. Emotional stress and excitement may also provoke hiccups in some people.
Ear, Throat and Esophageal Irritation
Ear, throat and esophageal conditions that irritate the vagus or phrenic nerves, which control some of the functions of these structures, may lead to hiccups. According to MayoClinic.com, possible causes include gastroesophageal reflux, laryngitis, sore throat, neck tumors or cysts, thyroid enlargement, ear infections and a hair or another foreign object touching the eardrum.
Chest Disorders
In a National Library of Medicine Medline Plus entry, Dr. Linda Vorvick points out that chest disorders can irritate the nerves of the diaphragm, stimulating hiccups. Possible causes include pneumonia, pleurisy, chest tumors, pericarditis, heart attack, hiatal hernia and thoracic aortic aneurysm--a bulge in the main artery carrying blood from the heart.
Brain and Nerve Disorders
Hiccups involve a complex series of signals between the brain, diaphragm and glottis. Brain and nerve disorders that cause increased signaling or loss of control along these pathways may provoke protracted episodes of hiccups, notes MayoClinic.com. Possible causes include stroke, nervous system tumors, encephalitis, meningitis, multiple sclerosis and traumatic brain injury.
Metabolic Disorders and Medication
Certain metabolic imbalances and medications can trigger hiccups. In a National Library of Medicine Medline Plus entry, nephrologist Parul Patel, M.D., notes that persistent hiccups can be a symptom of acute kidney failure. Other possible metabolic causes of prolonged hiccups include potassium deficiency, sodium deficiency, chronic kidney failure, abnormally high or low blood sugar and adrenal hormone deficiency. Medications that may provoke hiccups include methyldopa, dexamethasone and other steroid medications, narcotic pain relievers and benzodiazepines.
