Initially, visible light lasers and IPL devices were used to tighten the skin with the help of Skin Rejuvenation Devices. According to popular belief, specially designed lasers in the mid-to-near infrared spectrum of light will bypass the outer layers of skin and penetrate deep into the dermis, depositing energy and denature proteins. Skin Rejuvenation Devices heat then stimulates collagen proliferation, resulting in a thickening of the healthy skin layers and gradually removing superficial wrinkles from the skin. A second theory is that by targeting and injuring microcapillaries, visible light lasers and IPLs increase their permeability, causing the release of inflammatory mediators. These mediators then stimulate fibroblasts to produce collagen, which reduces wrinkles.