Immunology is a branch of biomedical science that covers the study of immune systems in all organisms. It charts, measures, and contextualizes the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders such as autoimmune diseases, hypersensitivities, immune deficiency, and transplant rejection; the physical, chemical and physiological characteristics of the components of the immune system in vitro, in situ, and in vivo. Immunology has applications in numerous disciplines of medicine, particularly in the fields of organ transplantation, oncology, virology, bacteriology, parasitology, psychiatry, and dermatology.