A foam delivery system comprising: (i) a solvent composition selected from the group consisting of water, a volatile propellant, a fluid C1-C6 alkyl or branched alkyl alcohol, an aromatic alcohol, an ether of a derivative of sorbitol, propylene carbonate, xylene, methylene chloride, ethylhexanediol, polysiloxanes, dimethyl ether, and mixtures thereof； (ii) a surfactant composition that is a fatty acid or a pharmaceutically acceptable salt thereof； (iii) a propellant selected from the group consisting of propane-butane, propane-isobutane-butane, isobutenobutane, petroleum gases, chlorofluorocarbons (CFC's), hydrofluoroalkanes (HFA's), dimethyl ether, propanoisobutane, isobutene, compressed oxygen, compressed hydrogen, compressed nitrogen, compressed nitrous oxide, methylene chloride, and mixtures thereof； and (iv) an acid in an amount that affects the pH of the administration system, selected from the group consisting of: (a) acetylsalicylic acid, ascorbic acid, boric acid, carbonic acid, formic acid, ethanesulfonic acid, fumaric acid, acid glycerophosphoric acid, hippuric acid, hydrochloric acid, maleic acid, methanesulfonic acid, nitrous acid, oxalic acid, phosphoric acid, saccharin, sorbic acid, sulfuric acid, thiosulfuric acid, undecylenic acid, ethanolamine, and one of its salts, esters, or solvates pharmaceutically acceptable； (b) an alpha hydroxy acid of the formula I: (Ra) (Rb) C (OH) COOH I or a pharmaceutically acceptable salt, lactone, or solvate thereof, in which Ra and Rb are independently selected from the group consisting in H, F, Cl, Br, and saturated or unsaturated C1-C25 alkyl, isomeric or non-isomeric, linear, branched, or cyclic, aralkyl, or aryl groups, in which each of Ra and Rb may be optionally substituted with a group OH, SH, CHO, COOH； (c) an alpha keto acid of formula II: (Ra) COCOO (Rb) II or a pharmaceutically acceptable salt, ester, or solvate thereof, in which Ra and Rb are independently selected from the group consisting of H and alkyl
