We study the primary photolysis dynamics of lactic acid induced by excitation at λ = 200 nm with the aim of elucidating how simple aqueous carboxyl acids react to the deep ultraviolet exposure on the prebiotic Earth. UV-IR transient absorption spectroscopy shows a photolysis quantum yield of Φ(100 ps) = 100 ± 5%. The primary products are CO₂, CO₂˙⁻ and their counter products CH₃CHOH˙ and CH₃CHOH⁻. DFT calculations suggest that the dissociation takes place from the strongly acidic nπ* excited state. Dehydroxylation of lactic acid is not observed.