Chapter 10: Acids and alkalis · Part 2: Acids
Lactic acid
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The worst fact: Australia classes it as "Causes serious eye damage", and the L-form as "Causes severe skin burns and eye damage". In leave-on skin creams, alpha hydroxy acids (the family that includes lactic acid) raise sun sensitivity: in a US FDA study of glycolic acid, skin reddened 18% more easily under UV after 4 weeks.
Why brands use it: it removes scale and is a registered disinfectant in the US for hard surfaces.
Take care if: you get it in your eyes, have stone benches, or use lactic-acid skin products in the sun. The sun effect is from leave-on skin products, not rinse-off cleaners, and it fades within a week of stopping.
Comes from: sugars such as glucose, molasses or whey, fermented. It can also be made synthetically from acetaldehyde, which Australia classes as "May cause cancer", but about 90% is made by fermentation.
Myth check: "A natural acid can't disinfect": it can. Lactic acid is registered as a disinfectant in the US.
Contaminants: nil.
Fair to say: it occurs naturally in fermented milk. In the US it's allowed in food (except infant food) with no set limit.
Correct as of November 2026. What the badges mean
Sources
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for ethylene oxide, carbon monoxide and acetaldehyde.
- US EPA. Chemical Safety Alert: safe storage and handling of swimming pool chemicals (2001); Federal Register 74:26692 (L-lactic acid, 2009).
The full source list is at the end of Chapter 10.