5-aminolevulinic acid is the simplest delta-amino acid in which the hydrogens at the gamma position are replaced by an oxo group. It is metabolised to protoporphyrin IX, a photoactive compound which accumulates in the skin. Used (in the form of the hydrochloride salt)in combination with blue light illumination for the treatment of minimally to moderately thick actinic keratosis of the face or scalp. It has a role as a photosensitizing agent, an antineoplastic agent, a dermatologic drug, a prodrug, a plant metabolite, a human metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite. It is a delta-amino acid and a 4-oxo monocarboxylic acid. It is functionally related to a 4-oxopentanoic acid. It is a conjugate base of a 5-ammoniolevulinic acid. It is a conjugate acid of a 5-aminolevulinate. It is a tautomer of a 5-ammoniolevulinate.