Why is humidity a factor in ammunition storage?

Humidity is a crucial factor in ammunition storage primarily because high humidity can lead to rust and corrosion. Ammunition typically contains metal components, such as the casing and the bullet itself. When exposed to high levels of moisture in the air, these metals can oxidize, leading to rust. Rust not only degrades the physical structure of the ammunition, potentially making it unreliable or unsafe to use, but it can also affect how the ammunition performs when fired.

This is particularly important for firearm owners who may store ammunition for extended periods. Ensuring proper humidity levels in storage environments helps maintain the integrity and reliability of the ammunition. In contrast, the other options do not address the critical aspect of how high humidity directly impacts the ammunition's performance and longevity.