劣化

Refers to the decline in quality, performance, or physical integrity of a material or system over time. It is most commonly used in technical, scientific, or industrial contexts to describe chemical breakdown (like rubber cracking) or the loss of fidelity in digital signals and images.

Unlike "低下" (teika), which refers to a drop in levels, numbers, or general ability (e.g., temperature or productivity), "劣化" specifically targets the inherent quality or structural integrity of an object or a specific performance metric.

Similarly, while "悪化" (akka) describes a situation or condition becoming worse (e.g., weather or a medical condition), "劣化" is reserved for the degradation of a physical substance or a functional specification.

In modern slang or casual conversation, it is sometimes used hyperbolically to describe a person's appearance aging or a sequel to a movie being inferior to the original, though this is a departure from its formal technical meaning.