Citric acid is a relatively weak acid, according to the pH calculator at Sensorex.com, and will not burn human skin like stronger acids. According to the Global Healing Center, though, it does contain high levels of MSG that can contribute to obesity and associated health problems.
According to SensoreX.com, a chemistry reference website, a solution of 100 percent citric acid carries a fairly low pH of 1.57. In the state found in common food items, though, natural citric acid solutions carry a pH of about 6.
Citric acid occurs naturally in most citrus fruits. In addition, many organisms produce some amount of citric acid during the natural metabolic process.
Some food processors add citric acid to sodas and other food items to add a fizzy kick to the taste of food.
In addition to serving as a food additive, citric acid appears in many cleaning solutions due to its acidic---but relatively safe---functionality.