Citric Acid

What it is

Citric acid is the substance used in cosmetics to set the pH value. It therefore appears in almost every shampoo, usually right at the end of the ingredient list. Hair and scalp are naturally slightly acidic; cleansing, colouring and reshaping push the pH upwards. Citric acid brings it back down.

The second function is often the more important one in the salon: citric acid binds metal ions. Calcium and magnesium from hard water, iron and copper from pipes deposit on the hair and interfere both with the colour result and with the stability of a formulation. Products that advertise decalcifying work with exactly this property.

Why

• Origin corrected: until this assessment the short field named citrus fruit as the origin. That does not apply to the citric acid used technically. For around a hundred years it has been produced by fermentation with the mould Aspergillus niger and not extracted from fruit. The short field was therefore changed to “produced by fermentation” in all four languages.
• The manufacturing route changes nothing about the molecule. Citric acid obtained by fermentation is identical to the one from a lemon. Precisely for that reason origin plays no part in the result of this assessment — it is corrected as factual information, not as a judgement.
• Why the classification reads “very low risk”: citric acid is a weak organic acid that occurs in the metabolism of every human cell. In hair products it is present in small amounts and serves to bring the pH into the slightly acidic range — where skin and hair sit anyway. Rinse-off use and short contact time come on top of that.
• What matters is not the substance but the pH value that is set. The same acid can irritate the skin at high concentration and is used in skincare as a fruit acid to remove the uppermost horny layer. In the role of a pH regulator that is precisely not intended. The role cannot be read from the ingredient list — a position right at the end is an indication, not proof.
• The most important point in practice is the binding of metal ions. Free traces of iron and copper accelerate the decomposition of hydrogen peroxide and lead to uneven colour and lightening results. Citric acid captures part of them. How large that part is in a specific product depends on the amount and on water hardness and is stated nowhere.

When the assessment differs

• Irritated or broken scalp skin: every acid stings on injured skin. After bleaching or with existing eczema that is a practical point, not a toxicological one.
• Eye contact: acidic preparations irritate the eyes more than neutral ones. Relevant with children and when washing backwards over the basin.
• Products that stay on skin or hair: the assessment assumes rinse-off use. In leave-on products the pH value that is set counts for more.
• Very soft or very hard water: with hard water the decalcifying capacity is called upon and the acid is consumed faster; with soft water the same amount has a stronger effect on the pH.
• Mould allergy: the question comes up regularly because of the manufacturing route. The finished substance is a purified chemical and not a fungal component; residues from fermentation have not been checked here and are not asserted second-hand.

Open questions

• Concentration and the pH value actually set in the specific product: not available. Both determine tolerability more than the substance itself.
• Purity of the raw material used and possible residues from fermentation: not documented and not readable from the ingredient list.
• Share of metal binding in the overall effect of a decalcifying product: cannot be quantified. Such products usually contain several chelating agents side by side.
• Regulatory status: not checked; statements on use and maximum levels are not quoted second-hand.

Sources for this assessment

• Latif A. u. a.: An overview of key industrial product citric acid production by Aspergillus niger and its application. Journal of Industrial Microbiology and Biotechnology, Band 52, 2025, kuaf007. Begutachtete Übersichtsarbeit, offener Zugang, abgerufen am 10.09.2026.

Related substances

Applies to: Alkalising and pH-adjusting agents

• Aminomethyl Propanol — Formulation ingredient
• Ammonium Bicarbonate — pH buffer, alkalising
• Ammonium Hydroxide — Alkalising agent

Further substances from the same group for which a long-form assessment already exists.