Citric acid

Citric acid is probably the most frequently printed additive name in your kitchen. It sharpens soft drinks, keeps tinned fruit from discolouring, balances the pH of jams and cosmetics, and turns up in cleaning products for the same chemical reasons.

The name suggests it was squeezed out of citrus. For over a century, mostly, it has not been.

What the regulation actually says

The US definition is unusually frank about manufacturing. Citric acid, it says, “may be produced by recovery from sources such as lemon or pineapple juice; by mycological fermentation using Candida spp.”; or by recovery “from Aspergillus niger fermentation liquor.”

That last route is the industrial standard: a mould, fed on a sugar source, produces citric acid in quantities no orchard could. Lemon juice is in the regulation as history rather than as practice.

This is worth seeing plainly written down, because both of the worries this ingredient attracts start from not knowing it.

The citrus allergy worry

A citrus allergy is a reaction to proteins in citrus fruit. Fermentation-produced citric acid is not made from citrus and carries no citrus protein, so the name is pointing you at the wrong thing: the molecule is identical wherever it came from, and the allergy is not to the molecule.

The honest caveat is the same one that runs through this whole site: almost always fermentation is not always, and the ingredient list does not say which route a particular batch took. If your reaction history makes that distinction matter, that is a conversation for your allergist, and the manufacturer can answer the route question where a label cannot.

The mould worry

The other direction of concern, common in scare content, is exactly the opposite: that citric acid is alarming because it is made with a black mould.

The useful facts are that the regulation names the organism openly rather than concealing it, that the purification and recovery steps are themselves part of the approved processes it cross-references, and that the finished ingredient is the acid, not the organism. An ingredient made by fermentation is not a fermented ingredient in the finished product, in the same way that Monosodium glutamate and the fermentation-produced version of Rennet do not carry their production organisms with them.

On skin

Citric acid appears in cosmetics mostly as a pH adjuster, present in small amounts to keep a formulation where it should be, and sometimes at higher concentrations as an exfoliating acid in the same family as Salicylic acid’s neighbours. The difference between those two uses is the difference between not noticing it and noticing it immediately, and the ingredient list does not carry percentages. If your skin reacts to acids, the product type is a better clue than the ingredient’s presence, and the wider version of that reasoning is on the page for skin that reacts to everything.