Necrobiosis is natural cell and tissue death. Cells and tissue are in a constant state of renewal and this process is normal. In some settings, people may use the term “necrobiosis” to refer to cell and tissue death caused by disease and other processes, even though these are not necessarily normal. An example of this usage can be seen in the condition necrobiosis lipoidica, a dermatological disease most commonly seen in people with diabetes where rashes form on the lower legs because the cells are dying.
The body is highly efficiently organized. When cells outlive their usefulness because of aging or use, a breakdown process is set in motion to allow the cell to die and then rupture, releasing its contents into the bloodstream. The contents of the cell are filtered out, with usable components being recycled to make new cells, while waste materials are transported out through the urine. In some cases, dead and dying cells may stick around, as seen with the skin, where the upper layers contain dead cells that slough away as new cells grow underneath.
At any given time, necrobiosis is occurring all over the body. The cells continually turn over and renew. Certain things can cause the schedule to be accelerated, such as injuries that trigger the formation of new cells for the purpose of repairing a damaged site, and certain conditions that lead people to break down cells or make new cells more quickly than usual.
The natural process of cell death provides a mechanism for replacing cells that are not functioning any more. In multicellular organisms, this allows the organism as a whole to continue living even as individual cells die and are replaced. The body can also target cells for destruction if it identifies them as diseased or otherwise compromised, in a process known as apoptosis. In this case, a cell death is triggered by the presence of certain characteristics that act like a red flag warning to indicate that there is a problem with the cell.
Necrobiosis can be accompanied with necrosis, when tissue and cells die sooner than they are supposed to. Necrosis can be the result of disease, confused signals sent by cells, and trauma to the cells. Treatment usually involves debriding or removing the dead tissue to expose the healthy tissue growing underneath, and managing conditions to keep the living cells healthy. Antibiotics may be applied to kill infectious organisms, for example, and the site may be covered with a bandage to limit exposure to harmful things in the environment.