Pathological twists in association with infectious agents and infestations of the skin

The capacity of micro-organisms and infestations to induce flare or mimic a wide variety of dermatological disorders has long been appreciated. The development of new techniques such as in situ hybridization and the polymerase chain reaction has permitted a re-examination of old concepts such as the tuberculids and bacterids. In addition new discoveries have highlighted the biological potential of micro-organisms to stimulate or depress the immune system through potent biological active products and has led to new insights in the mechanisms through which organisms may produce skin changes. Histological simulants of dermatological disease may also be induced by micro-organisms and these may need to be distinguished by clinical correlation.