Egg cells need stamina: They are formed in a woman’s body before birth and have to be on standby for decades to possibly be fertilized one day. But as they age, they accumulate more and more DNA damage. Until now, it has been unclear why the cell’s repair mechanisms do not fix the damage. Researchers led by Melina Schuh and Ninadini Sharma at the Max Planck Institute (MPI) for Multidisciplinary Sciences in Göttingen (Germany) have now shown in experiments with mice that aged egg cells repair their DNA less efficiently than young ones, and that repair becomes more error-prone with advancing age.