During the G₁ phase of the cell cycle, a cell checks for the availability of growth factors and nutrients. If the necessary resources are not available, the cell can exit the cell cycle and enter the G0 stage, which is a non-dividing, metabolically inactive phase. Cells in the G₀ stage may stay in this phase temporarily or permanently, depending on the cell type and environmental conditions.

Some cells in the G₀ stage, such as neurons and muscle cells, remain in this phase permanently and do not re-enter the cell cycle, whereas other cells, such as liver cells and lymphocytes, can re-enter the cell cycle in response to specific signals or stimuli.