Saliva contains a natural buffer (bicarbonate) that neutralizes acid in the esophagus. If salivary production is reduced, its protective capabilities are compromised.

The esophagus is a muscular tube that squeezes food towards the stomach (much like squeezing a tube of toothpaste). This muscular action is called peristalsis. It keeps what we ingest moving in the right direction.
Impaired esophageal peristalsis allows things to move in the wrong direction, such as stomach contents refluxing back into the esophagus.

Each part of the gastrointestinal tract has its own defense system to protect itself from stomach acid (as well as other irritants). If these defenses are compromised, the tissues lining these organs are vulnerable to injury from stomach acid. See Body’s line of defense against HCl for more.

• Reflux is especially prevalent in infants because the LES does not reach full maturity until 18 months of age.
• Transient LES relaxations (TLESR) are brief moments when the LES opens, giving way to the pressure of the stomach and allowing its contents to reflux into the esophagus.
• Many problems are due to a weak resting tone of the sphincter muscles, in which the LES cannot maintain a strong seal.

The muscular walls of the stomach have coordinated contractions to keep stomach contents moving through. If the stomach does not allow itself to empty as regularly as it should, pressure builds up within, pushing on the LES, making reflux much more likely.
Pyloric stenosis is one cause of delayed gastric emptying. This condition is a pathological narrowing of the lowest part of the stomach, or pylorus. This narrowing slows the rate at which food can leave the stomach, allowing pressure to build up in the stomach.

For the most part, reflux disorders do not mean that an excess of acid is being produced. Acid production still plays the major role, especially for patients who have already developed damage in their esophagus or stomach.
Acid production fluctuates during the day, but can flare up depending on diet, stress, or conditions such as teething. This tendency has great variability among patients.