Plastic Container Codes: A Comprehensive Guide to Their Uses, Risks, and Safety

In recent years, the widespread use of plastic containers for packaging and storing food has become a common choice in everyday life. Despite their ease of use and low cost, these containers can sometimes pose health risks—especially when certain plastics come into contact with hot, fatty, or acidic foods. In such cases, chemical compounds in the plastic may be released and transferred to the food. Some of these chemicals can have negative effects on the human body. Therefore, understanding the type of plastic and how to use it safely is essential. Identification codes and the recycling triangle symbol can serve as helpful tools for making healthier choices.

The Recycling Triangle

In the 1970s, environmental movements began forming around the world. These movements aimed to raise public awareness about environmental issues like air pollution, plastic waste, deforestation, and climate change. As industries grew and mass-produced plastic materials, a large amount of this waste remained in nature, taking hundreds of years to decompose. As a result, many countries and organizations began seeking more sustainable solutions like recycling.

One of the leading cardboard packaging companies in the U.S. launched a design contest to support environmental movements and promote recycling. The goal of the competition was to create a symbol that would widely communicate the importance of recycling. Gary Anderson, a student at the University of Southern California, designed the now-famous three-arrow recycling symbol, inspired by the Möbius strip—a unique geometric shape with only one surface and one edge. His design won the competition and quickly became one of the most recognized environmental icons.

Plastic Recycling Codes

Plastic identification codes, also known as Resin Identification Codes (RIC), were introduced in 1988 by the Society of the Plastics Industry (SPI) in the United States. These codes include numbers from 1 to 7, each representing a specific type of plastic.

The main purpose of this system was to simplify the sorting and categorization of plastics for better recycling. Initially, the codes were created to help workers at recycling centers identify the plastic type and optimize the recycling process.

Today, these codes help consumers understand what material a product is made from, how to use it safely, and what risks it may carry. By paying attention to these codes, consumers can make better choices about plastic use.

Code 1: Polyethylene Terephthalate (PET or PETE)

Polyethylene terephthalate is a type of plastic made from two chemical substances: terephthalic acid and monoethylene glycol. Due to its properties—such as light weight, high transparency, and impact resistance—it is widely used in food and beverage packaging industries.

• Common Uses

Water bottles, soda bottles, juice containers, packaging for fruits and vegetables, and containers for products like peanut butter and mayonnaise are usually made from PET. Thanks to its mechanical strength, transparency, moisture and gas resistance, and ease of production, PET is ideal for liquid packaging. It is also highly recyclable, which adds to its popularity.

• Health Risks

Using PET containers is generally safe, but under certain conditions, harmful substances may leach out. One of these is antimony, a toxic metal used as a catalyst in PET production. When water bottles are exposed to sunlight or high temperatures (above 50°C), antimony may be released. Storing acidic liquids like vinegar or lemon juice in PET, or reusing the containers, can increase this risk.

Exposure to antimony can damage the liver and kidneys, cause heart problems, and potentially lead to cancer. It may also disrupt hormonal balance, affect weight regulation, and fertility

Some PET containers may also contain phthalates as plasticizers. These can disrupt hormones, reduce fertility, affect child development, and increase the risk of obesity and diabetes.

Code 2: High-Density Polyethylene (HDPE)

HDPE is a widely used polymer made from ethylene. It has a dense molecular structure that provides high strength and chemical resistance. It resists acids, alkalis, and solvents, and is lightweight and recyclable. However, recycling HDPE can be more complicated due to the additives it sometimes contains.

• Common Uses

HDPE is commonly used for milk jugs because it helps prevent light and moisture penetration, preserving freshness. It's also used for some non-transparent water bottles, yogurt containers, produce bags, and detergent bottles. Its moisture resistance and durability make it suitable for packaging dairy and other foods.

• Health Risks

HDPE is generally considered safe, especially for cold, non-acidic foods. However, colored HDPE may contain benzophenones as UV stabilizers. If exposed to sunlight or high heat, these can break down and migrate into food, potentially disrupting hormones, causing reproductive issues, and increasing cancer risk.

Some colored HDPE containers may also contain heavy metals like lead and cadmium. These can leach into food at high temperatures (above 120°C). Lead is highly toxic to the nervous system and may cause cognitive issues and memory damage. Cadmium is a carcinogen that accumulates in the body and can harm kidneys, the nervous system, and the immune system.

HDPE may also contain triazines used for UV protection, which can break down and leach into food at high temperatures. Additionally, ethylene monomers may be released under extreme conditions, leading to risks like poisoning, neurological issues, and respiratory problems.

Code 3: Polyvinyl Chloride (PVC)

PVC is made from vinyl chloride monomers and is known for its moisture, chemical, and corrosion resistance. Naturally rigid, it becomes flexible when plasticizers are added. There are two types of PVC: rigid (used where strength is needed) and flexible (used where bending is required). PVC is difficult to biodegrade and can release toxic chemicals when burned.

• Common Uses

PVC is used in plumbing pipes, window frames, toys, shower curtains, and some food packaging like cling films. It’s also found in single-use containers and beverage bottles due to its light weight and flexibility.

• Health Risks

PVC can release harmful chemicals under certain conditions:

• Phthalates

These plasticizers increase flexibility but may leach into fatty foods, especially at temperatures above 50°C. They can disrupt hormones, reduce fertility, affect child development, and increase the risk of obesity and diabetes.

• Vinyl chloride

This toxic monomer can be released during burning or improper recycling. It is classified as a human carcinogen by the U.S. EPA and is dangerous when inhaled.

• Dioxins

These toxic compounds are released during PVC burning or improper recycling and are linked to cancer, immune system issues, and reproductive harm.

• Heavy Metals

Lead and cadmium are sometimes added as stabilizers and can leach into food at high temperatures. They are toxic and associated with cancer, kidney damage, and neurological problems.

Code 4: Low-Density Polyethylene (LDPE)

LDPE is a type of plastic known for its high flexibility, low weight, and resistance to tearing and impact. It can easily bend and stretch, and it resists many chemicals, acids, and bases. However, LDPE often contains additives that make recycling more complex, and it is less commonly collected in standard recycling systems.

• Common Uses

LDPE is widely used in food packaging—especially for plastic bags that hold bread, fruits, and vegetables. These bags are ideal for lightweight and flexible packaging. It's also used in squeeze bottles for sauces like ketchup and mayonnaise, as well as in protective food wraps that prevent moisture and air penetration.

• Health Risk

LDPE is generally safe at room temperature. However, at higher temperatures (above 70°C), especially when heating fatty foods, chemical additives may be released into the food. These include:

Antioxidants like BHA and BHT: Added to prevent plastic degradation, these may cause digestive issues such as nausea and vomiting. BHA is classified by the IARC as a possible human carcinogen (Group 2B).

Note: The antioxidants used in plastic containers are different from the natural antioxidants found in fruits and vegetables.

Plasticizers like DBP and DEHP: Used to increase flexibility, these can disrupt hormones, impair growth and development, damage the liver and kidneys, and affect the endocrine and nervous systems.

Ethylene monomer: May be released under prolonged sunlight exposure, leading to potential toxicity, neurological, and respiratory problems.

Code 5: Polypropylene (PP)

PP is a widely used plastic in food storage and packaging because of its high heat resistance and strong chemical resistance to acids, bases, and some solvents. It also has low permeability to moisture and gases, which helps preserve food quality.

• Common Uses

PP is used in freezer containers, food storage containers, and packaging for dairy and acidic foods. It is particularly suitable for microwave use because it can tolerate temperatures above 130°C with minimal risk of releasing harmful substances.

• Health Risks

Polypropylene is generally considered a safe plastic; however, it should be avoided in certain conditions that may lead to the release of harmful substances.

• Exposure to Sunlight

To prevent damage to the UV stabilizers, it is advisable to store polypropylene containers away from direct sunlight.

• Prolonged Use in Microwave

These containers are not suitable for cooking or prolonged heating. When used to heat food in a microwave, the heating time should be kept short (for example, around 3 minutes). This helps reduce the risk of releasing harmful chemicals.

• Optimal Use of Polypropylene Containers

If polypropylene containers are repeatedly used to store acidic or fatty foods, or for reheating, it is recommended to replace them if visible changes appear, such as discoloration or scratches. These signs may indicate degradation of the plastic structure, which can lead to the release of harmful substances and potential health issues.

Code 6: Polystyrene (PS)

Polystyrene is a lightweight, transparent, and easily moldable plastic made from the chemical styrene. It is inexpensive and widely used in many industries.

• Common Uses

PS is commonly used for disposable cups, plates, and food containers. It is also found in food packaging, especially for frozen goods, beverages, and takeout. It works well at low temperatures and is often used for packaging meat, poultry, and fish.

• Health Risks

Polystyrene, especially at high temperatures (around 70°C or higher) or when in contact with fatty substances, can release chemicals that may be harmful to human health. For example, styrene, the monomer used to produce this plastic, can leach out of polystyrene at high temperatures (such as when heating food in a microwave) or when in contact with hot, fatty foods. This chemical has negative effects on the nervous system, which may include symptoms such as headaches, dizziness, and fatigue.

Styrene is also classified as a possible human carcinogen (Group 2A), and prolonged exposure may increase the risk of developing certain types of cancer.

In addition, plasticizers added to polystyrene to increase its flexibility—such as di-octyl phthalate (DOP) and di-octyl terephthalate (DOTP)—can also be released at high temperatures or when in contact with fatty substances. These chemicals may negatively affect the hormonal system, leading to fertility issues and hormonal imbalances, and may also weaken the immune system. Over time, they could even contribute to cancer development.

Infants and young children are particularly sensitive to phthalates, and early exposure to these substances may result in behavioral problems, developmental delays, and hormonal disorders.

Code 7: Other Plastics

Code 7 refers to plastics that do not fall under the categories of codes 1 through 6. These plastics can be made from a variety of materials, including polycarbonate and biodegradable plastics such as polylactic acid (PLA). These containers are generally considered safe for short-term use, such as storing cold water for a few hours, but they are not resistant to high temperatures and should not be exposed to heat.

Recycling these plastics is challenging, as the additives and plasticizers they contain complicate the recycling process. As a result, Code 7 plastics are rarely recycled and are more often discarded as waste. However, biodegradable plastics can break down under certain conditions when exposed to environmental factors such as microorganisms.

• Common Uses

Code 7 plastics have several common applications in the food industry. These include reusable water bottles, certain food storage containers, and baby bottles. In addition, Code 7 plastics are also used in the production of single-use items such as plastic plates, cups, spoons, and forks.

• Health Risks

Code 7 plastics, especially polycarbonate, should be used with caution due to the presence of chemicals such as bisphenol A (BPA) and plasticizers. BPA is an industrial chemical used in the production of polycarbonate plastics. Under certain conditions—such as high temperatures or prolonged contact with food and beverages—BPA can leach into the contents.

For example, pouring hot food or drinks into these containers, storing acidic beverages like juice, or keeping food and drinks in them for extended periods can lead to BPA release, which poses several health risks. These include disruption of hormonal systems, infertility, early puberty, behavioral issues in children, obesity, diabetes, cardiovascular diseases, and even an increased risk of cancer.

Plasticizers can also leach out at high temperatures and may cause hormonal imbalances and developmental issues in children.

Additionally, colorants and additives used to enhance the appearance and durability of these plastics may contain heavy metals such as cadmium and lead, which can cause neurological, liver, and kidney problems, and are also linked to a higher risk of cancer.

If biodegradable plastics are broken down under unsuitable conditions, they may release microplastics, which are harmful to both the environment and human health. These particles can enter the environment and the aquatic food chain, eventually making their way into the human body, where they may cause digestive issues and hormonal disruptions. Furthermore, microplastics can lead to inflammation and weaken the immune system.

Final Word

Following safety guidelines when using plastic containers is essential to prevent the release of harmful chemicals. One common mistake is using single-use plastic containers for hot liquids. For example, using polystyrene (Code 6) or polyethylene terephthalate (PET, Code 1) with hot liquids may lead to the release of toxic substances such as antimony, which can negatively impact health. Moreover, repeated use of PET bottles (Code 1) can also result in antimony leaching over time.

Heating food in the microwave using inappropriate plastic containers like polystyrene (Code 6) or polyvinyl chloride (PVC, Code 3) can cause the release of toxic substances such as phthalates, which are associated with serious health risks.

Storing acidic or oily foods in certain Code 7 plastic containers can lead to the release of bisphenol A (BPA), a chemical linked to hormonal disruptions, cancer, and reproductive disorders.

To avoid these risks, it is recommended to use glass containers for storing and heating food. Glass is the safest option as it prevents the release of harmful chemicals. Among plastic containers, Codes 2 (HDPE), 4 (LDPE), and 5 (PP) are considered safer choices compared to others, but they are not completely risk-free. Therefore, it is important to follow safety precautions when using them.