What makes loose skin shrink to normal?

Elasticity: Once your skin has been stretched past its innate elasticity, only plastic surgery can tighten loose skin. Other treatments, such as rf (radio frequency), laser, or creams and lotions only provide minimal improvements. If your skin is youthful and you are not obese, your skin still has a unique degree of elasticity that would allow some degree of return to normal, as after pregnancy.

Elastin: Elastin is the substance in skin that give it the ability to stretch and snap back. Unfortunately as we age our skin loses much of it and the skin becomes less elastic. Various treatments seek to tighten the skin by heating it but the results are modest at best and temporary. Surgical excision which leaves scars is often the most effective.