A particulate laundry detergent composition which comprises a detergent base powder comprising surfactant and builder and, as separate particulate components:

• (a) an alkali metal carbonate salt selected from carbonate, bicarbonate, sesquicarbonate and combinations thereof; and
• (b) a water-soluble organic acid which, when reacted with (a) in the presence of water, generates carbon dioxide gas;

  wherein the alkali metal carbonate salt, when taken separately, has a 90% dissolution time of less than 15 seconds, preferably less than 10 seconds, more preferably less than 7 seconds; and the water-soluble organic acid has a d₅₀ particle size which is in the range of from 150 to 1500 microns. The alkali metal carbonate salt preferably has an average bulk density of at most 1000 g/l, preferably at most 800 g/l, more preferably at most 600 g/l. The alkali metal carbonate salt preferably has a d₅₀ particle size of at most 250 microns, preferably from 1 to 200 microns, more preferably from 10 to 150 microns. The alkali metal carbonate salt is preferably sodium and/or potassium carbonate.