The aging of whole organisms is called organismal senescence. In general, aging is characterized by the declining ability to respond to stress, increased homeostatic imbalance, and increased risk of aging-associated diseases. Death is the ultimate consequence of aging. Senescence occurs both on the level of the whole organism (organismal senescence) as well as on the level of its individual cells (cellular senescence). Senescence is by far the leading cause of death across the globe, in industrialized nations, the proportion is reaching 90%.