In situ foamable dental bleaching compositions include a dental bleaching agent, thickening agent, polyol, and in situ foaming agent. The foamable dental bleaching compositions are initially dispensed as a dental bleaching gel. Upon placement of the dental bleaching gel onto a person's tooth surfaces, the in situ foaming agent causes the bleaching gel to foam. Dental bleaching systems include an in situ foamable dental bleaching composition within a pressurized container (e.g., bag-on valve container) having a nozzle that, when actuated, expels the in situ dental bleaching composition as a gel. Dental bleaching methods include dispensing the in situ foamable dental bleaching composition as a gel, contacting a person's tooth surfaces with the dental bleaching gel, and allowing the gel to expand and foam in order to dynamically distribute and replenish the dental bleaching agent to the tooth surfaces and into the interproximal spaces between teeth.