Cells that undergo senescence display several changed features that can be used for identification. An increased secretory phenotype can be detected by measuring growth factors and cytokines. These factors contribute to the spreading of senescence to neighbouring cells or reinforce senescence via an autocrine process. Increased lysosomal activity can be detected using SA-β-Gal and SBB expression. Mitochondrial dysfunction is detectable by measuring ROS levels such as superoxide production. As cells undergo irreversible cell-cycle arrest, markers such as p16, p21 and p53 are increased while proliferation markers like Ki67 decrease. Resistance to apoptosis can be measured by changes in Bcl-2 and Bax expression. In addition, the DDR can be measured by immunofluorescence microscopy for increased formation of phosphorylated ATM and γ-H2AX in the nucleus. Abbreviation: SA-β-Gal, senescence-associated β-galactosidase.