A breaker composition for use in a fracturing fluid comprises water, at least one peroxide (e.g., tert-butyl hydroperoxide), and optionally at least one alcohol (e.g., propylene glycol and/or a butyl alcohol). The peroxide(s) and optional alcohol(s) are present in amounts effective to reduce the viscosity of a fracturing fluid at a temperature of 90-300 F. (the “breaking temperature”), and to prevent rehealing of the fracturing fluid, i.e., to maintain the reduced viscosity for a period of time after the temperature is reduced from the breaking temperature to a temperature below the breaking temperature (e.g., after the temperature is reduced from the breaking temperature to room temperature).