Abstract: Instant self-heating containers include a combinable reactant and activator used to generate an exothermic reaction for heating contents of the container. One instant self-heating container includes a target container, a pierceable activator container and a reaction chamber. Piercing the activator container causes activator to combine with the reactant and cause an exothermic reaction that heats the target container. The container may be used as depilatory wax dispenser. Another instant self-heating container includes an outer housing containing a contents pouch and a reactant, and capped by a lid having an activator chamber. Rupturing the activator chamber allows activator to combine with the reactant in an exothermic reaction to heat the contents pouch. Another instant self-heating container includes a flexible outer tube containing contents to be heated, a flexible reaction vessel, and a frangible activator vessel.