How Long Does It Take for a Plastic Bag to Decompose?

Every July, we’re reminded just how far small choices can go. Plastic Free July encourages us to look at what we toss, what we reuse—and what sticks around long after we’re done with it.

One of the worst offenders? The plastic bag.

These lightweight carriers are made for convenience but built to last. And that’s part of the problem. It raises an important question: How long does it take for a plastic bag to decompose? The answer reveals just how serious our plastic pollution problem really is—and why sustainable choices matter more than ever.

The Journey of a Plastic Bag: What Happens After Disposal

When a plastic bag is tossed, it begins a journey that often ends in one of three places: a landfill, a waterway, or an open dump. In each scenario, the decomposition timeline varies—but the outcome is consistently harmful.

In a landfill, the bag is sealed beneath layers of waste, away from air and sunlight. That slows the breakdown process dramatically. Even under better environmental conditions, it takes around 20 years for a single bag to fragment into microplastics. And that’s only the beginning of its pollution lifecycle.

If the bag escapes the landfill and reaches the ocean, its impact grows. It may resemble food to marine life, or simply break into pieces that enter the food chain—damaging ecosystems and human health along the way.

Landfill

Most plastic bags are buried in landfills, where they're sealed off with layers of clay and synthetic liners. While these barriers prevent chemical leakage, they also block oxygen and sunlight—two essential elements needed for breakdown. As a result, the type of plastic used in bags, usually polyethylene, can take decades to degrade. The decomposition process is extremely slow, and the bags remain intact for many years.

Waterway (rivers, lakes, or oceans)

If a bag escapes collection systems, wind or rain may carry it into nearby streams or storm drains, eventually reaching larger bodies of water. There, constant exposure to sun and motion breaks the bag into microplastics—tiny particles that pollute water, enter the food chain, and harm marine life. This is a major contributor to the estimated 11 million tonnes of plastic entering the ocean each year.

Open dumpsite

In areas without adequate waste management, plastic bags may be tossed in open landfills or informal dump areas. These sites offer no protection against wind, animals, or runoff. The bags mix with soil, leach toxins, and pose serious threats to wildlife and surrounding ecosystems. Unlike plastic cups or plastic water bottles, which may be captured through the recycling process, soft plastics like bags often go unmanaged and unprocessed.

Where Do Most Plastic Bags End Up in the United States?

Discarded plastic bags often end up in landfills throughout the United States. A single bag can remain trapped for decades, intact and harmful.

If the bag escapes waste collection, it may end up in rivers, lakes, or oceans. Over time, it breaks down into microplastics—tiny fragments that contaminate water, infiltrate the food chain, and contribute to serious ocean pollution. Marine animals often mistake these particles for food, which worsens the global plastic crisis and threatens ecosystems worldwide.

Factors Affecting the Decomposition Rate of Plastic Bags

How a plastic bag breaks down depends largely on environmental conditions. Sunlight, temperature shifts, and oxygen levels all play a role. In landfills—where light and airflow are limited—the decomposition process slows significantly compared to bags exposed to open air.

The type of plastic matters too. Most bags are made from polyethylene, a dense, durable material designed to last. This durability means it resists decomposition and can release harmful substances into the environment over time. These factors combined make plastic pollution difficult to manage—and even harder to reverse.

Climate, Sunlight, and Material Composition

Environmental variables, including climate, sunlight, and the makeup of the plastic, strongly influence decomposition rates. Intense sunlight can accelerate material breakdown through photodegradation, while subtropical or humid climates increase the rate of fragmentation due to warmth.

The relationship between conditions and decomposition becomes clear in the comparison below:

The above data underscores the role of external conditions and specific material types like polyethylene in determining how quickly plastic decomposes.

Why Are Plastic Bags So Difficult to Break Down?

Plastic bags are tough because the chemical bonds in them are strong. These bonds help the bags last a long time and keep goods safe. But they also make plastic hard to break down when people throw it away.

Microorganisms and fungi can not really break down these plastics. Most of them do not have the tools to eat away at these synthetic materials, so the bags barely change in nature. When these bags do slowly break apart into smaller pieces, they let out toxic chemicals that get into the ground, water, and nearby areas. This harms the ecosystems around them.

Some plastics also have extra chemicals called stabilizers. These additives make bags even harder for sunlight to break down. All of this makes it clear why plastic pollution is such a big problem. The mix of tough materials and the low chance of nature breaking them down means people need new ideas and better ways to deal with plastic waste.

Frequently Asked Questions

How long does it actually take for a plastic bag to decompose?

A regular plastic bag can take around 20 years to break down into tiny pieces—and even longer without sunlight or favorable conditions. This slow decomposition adds to the millions of tons of plastic already polluting our environment, highlighting just how serious the plastic crisis has become. It also makes waste management more difficult, especially as soft plastics continue to pile up faster than they break down.

Can biodegradable or compostable bags solve the problem with plastic waste?

Using biodegradable or compostable bags gives us hope to solve the problem of plastic waste. These bags can break down faster than normal plastic if you put them in the right place. This helps cut down on the issues we face with recycling. But these better bags still need to be thrown out the right way. They do not fully get rid of all the pollution that comes from using too many bags.

Are paper bags a better alternative to plastic bags?

Paper bags don’t contribute to long-term plastic pollution, but their production can result in a larger carbon footprint than plastic bags. This is because it takes a lot of energy to cut trees and process them into paper. Recycling helps, but they only become better for the environment when companies adopt responsible practices.

Examples of sustainability include using recycled materials, sourcing paper from certified forests, minimizing water use, and switching to renewable energy in production. These choices reduce the overall impact and make paper bags a more viable alternative.

What impact do plastic bags have on wildlife and marine life?

Plastic bags can hurt wildlife and marine life. These bags often break down and turn into microplastics, releasing toxins into nature. Many animals think plastic is food, or they get caught in it. This can make them sick and mess up the food chain. Because of plastic pollution, there are big problems for animals and their homes.

What can individuals do to reduce plastic bag pollution?

Americans can help fight plastic pollution by avoiding plastic bags and choosing reusable alternatives instead. Joining local cleanup efforts and staying committed to recycling at home and in your community are simple, powerful actions.

Supporting eco-friendly companies that prioritize sustainable packaging and invest in ocean cleanups—like those partnered with 4ocean—also makes a meaningful impact. Small daily choices, from reducing waste to rethinking how we consume, help us all move toward a cleaner, more sustainable future. Every action counts.