Not 'spoil', in its literal sense, they just undergo same harmful impacts as the rest of the body from junk food, smoking, etc. The fact that they dont regenerates in vivo, comparing with male counterpart, makes it looks like they 'spoil'.
Junk food and smoking a problem, but are far less of an issue than time itself.
Humans do not posses a time freeze energy field covering the ovaries.
People often think of bacteria and mold when they think spoiled food.
But sealed sterile foods like canned goods also spoil chemically with time. The same way that metal rusts/tarnishes over time, plastic and glue break down, etc. Take a look at a 40 year old car it just breaks down everywhere.
Chemical degradation of the structures of an egg happens.
Besides which there is cosmic radiation constantly bombarding the eggs and damaging their DNA
But yes smoking and junk food ALSO harm it.