Infectious development is a photographic process observed when developing "lith" materials, where the chemical reactions amplify themselves. During this process, the oxidation of hydroquinone generates highly active reducing agents called semiquinones in the presence of a small amount of sodium sulfite. These agents accelerate development in surrounding areas, producing images with extremely high contrast.
This technique is primarily used in specialised black-and-white photographic processes to achieve dramatic tonal effects and enhanced edge definition. Understanding infectious development helps photographers working in alternative or experimental darkroom methods control contrast and achieve striking visual results.