For pepsin to be as active as possible, it requires temperatures around 98 to 107 degrees Fahrenheit. Additionally, it is most active in acidic environments of between pH 1.5 to 2. In environments of pH 6.5 or above, pepsin becomes inactive. Around pH 8, pepsin becomes permanently inactive. Because pepsin is so stable even at high pH levels, it can remain in environments such as the larynx following gastric reflux. Typically, the pepsin is inactive without the presence of the gastric acid. However, another reflux event would activate the pepsin and damage the surrounding tissue.

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