A method and system for skin tightening comprises a hollow cannula that contains an optical fiber connected to a laser source. The cannula is inserted subcutaneously into a patient so that the end of the fiber is located within the tissue underlying the dermis. The source emits an output pulse that is conveyed by the fiber to the dermis, where the pulse causes collagen destruction and shrinkage within the treatment area. Radiation from the skin surface is detected to prevent non-reversible damage to the dermis, such as skin necrosis and excessive collagen melting. This method of sub-cutaneous laser treatment can also be used to treat striae, or stretch marks.
