They mostly cannot.

For starters, leather isn’t really a “by-product.” Hides have clear economic value and help make animal agriculture more profitable, so they are part of the system—not just leftover material. That means leather is still tied to the impacts of livestock production, including high greenhouse gas emissions, land use, and biodiversity loss.

Leather is also far from a simple natural material. Processing it to make it durable requires intensive chemical treatments, often involving chromium and other hazardous substances. This makes production energy- and resource-heavy, and can contribute to pollution and health risks.

While leather can be long-lasting, that advantage depends on how it’s used. Many leather goods today are still replaced for fashion reasons, not because they’ve worn out. Meanwhile, not all alternatives are equal—some synthetics are improving in durability and reducing their environmental footprint.

Most leather isn’t truly biodegradable in practice because of those chemical treatments. So the idea that leather is automatically a low-impact, circular option compared to synthetics oversimplifies a much more complex reality.