Citric Acid: What It Is and Why It's Used

Origin

Citric acid was first isolated from lemon juice by Carl Wilhelm Scheele in 1784. Industrial production through fermentation by Aspergillus niger was developed in the early 20th century, as citric acid demand for food and beverage use outstripped what could be extracted from citrus fruit. Today essentially all commercially used citric acid is produced by microbial fermentation rather than fruit extraction.

Why It's Used

In hair care formulations, citric acid is used primarily as a pH adjuster — it lowers pH to a range (4.5–5.5) that keeps the hair cuticle closed and smooth, reducing frizz and improving shine. It is also a chelating agent, binding to metal ions (particularly calcium and magnesium from hard water) that can accumulate on the hair and dull its appearance. At high concentrations it functions as an AHA, but this is not the relevant function in most hair care products.

Elsewhere

Citric acid is one of the most widely used food additives globally — used as a flavouring and preservative in beverages, confectionery, and processed foods. It is used in pharmaceuticals, in cleaning products as a descaling agent, and in industrial processes as a metal chelator.

What the Framework Sees

Question 1, with a useful exception to the usual reading.

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