Based on available research, tears are typically not acidic. Instead, they are slightly alkaline.
Research into the composition of human tears provides insight into their pH levels. A notable study by Carney and Hill, published in the Archives in May 1976 (94:821-824), examined the pH of human tears under different conditions.
Key Findings on Tear pH
According to the study:
- Tears collected from an unopened eye in the morning were found to have an average pH of 7.25.
- Tears collected later in the day had a slightly higher average pH of 7.45.
Understanding the pH Scale
The pH scale measures how acidic or alkaline a substance is:
- A pH of 7.0 is considered neutral (like pure water).
- A pH below 7.0 is acidic.
- A pH above 7.0 is alkaline (or basic).
Are Tears Acidic?
Based on the data from the Carney and Hill study:
- The average morning tear pH (7.25) is above 7.0.
- The average later-day tear pH (7.45) is also above 7.0.
Both of these values fall into the alkaline range of the pH scale. While the study notes that morning tears (pH 7.25) are "more acid" than later tears (pH 7.45), this is a relative comparison meaning the morning tears are closer to the neutral point (pH 7.0) compared to the later tears, but they are still on the alkaline side of the scale.
Therefore, according to this research, human tears are slightly alkaline, not acidic.
