The extracellular matrix (ECM) surrounds and supports cells, both structurally and in a range of other ways, such as by mediating cell signalling. With age, however, the ECM changes for a variety of reasons - it is damaged by the actions of senescent cells, for example. This has consequences, such as on the capacity of stem cells to maintain tissue. Here is a review paper: "Aging is characterized by reduced tissue and organ function, regenerative capacity, and accompanied by a decrease in tissue resident stem cell numbers and a loss of potency. The impact of aging on stem cell populations differs between tissues and depends on a number of non cell-intrinsic factors, including systemic changes associated with immune system alterations, as well as senescence related changes of the local cytoarchitecture. The latter has been studied in the context of environmental niche properties required for stem cell maintenance. Here, we will discuss the impact of the extracellular matrix (ECM) on stem cell maintenance, its changes during aging and its significance for stem cell therapy. ... It is concluded that a remodeled ECM due to age related inflammation, fibrosis or oxidative stress provides an inadequate environment for endogenous regeneration or stem cell therapies." The question of whether an old body can fully benefit from stem cell therapies continues to arise - eventually the stem cell research community will have to start addressing the damage of aging in order to assure the performance of their therapies when treating the old.