Plastic containers contain many chemicals, some of which have been identified as potentially harmful. You should avoid two chemicals in particular: bisphenol A and phthalates. Both of these chemicals interfere with animal and human hormones.
Researchers have better identified the harmful effects of bisphenol A; pthalates are generally considered safe by comparison. Still, better safe than sorry. Whether a plastic container has bisphenol A or phthalates in it depends on its type. You can identify the type of plastic in a container by looking at the recycling code number.
Type 1: Polyethylene Teraphthalate - Do Not Reuse
You commonly find Type 1 plastic in bottles for juices, salad dressing, water, vegetable oil and mouthwash. Peanut butter and pickle jars often contain type 1 plastic as well. Polyethylene teraphthalate is light-weight, clear and smooth; its manufacturers intend it for a single use only.
While it does not contain bisphenol A or phthalates, it does contain antimony, a possible human carcinogen. Also, harmful bacteria can build up in it as you reuse it. Polyethylene teraphthalate containers may have the symbol "PET" on them.
Type 2: High-Density Polyethylene - Safe
Milk containers, detergent bottles, freezer bags and plastic grocery bags often contain high-density polyethylene, a relatively stiff plastic. Type 2 plastic neither contains bisphenol A nor phthalates. It is not known to contain other harmful chemicals. High-density polyethylene containers may have the symbol "HDPE" on them.
Type 3: Polyvinyl Chloride - Contains Phthalates
Polyvinyl chloride contains phthalates that can cause reproductive problems in animals and humans. Type 3 plastic can be plasticized or unplasticized; the former is clear and flexible, the latter is more rigid. Food containers commonly made with polyvinyl chloride include fruit juice bottles, cooking oil bottles and clear food packaging. Plasticized PVC pipes and siding contain phthalates as well. Polyvinyl chloride containers may have the symbol "V" on them.
Type 4: Low-Density Polyethylene - Safe
Frozen foods packaging and condiment squeeze bottles often contain Type 4 plastic because it is flexible and resistant to solvents. Type 4 plastic does not contain any known harmful chemicals. Low-density polyethylene containers may have the symbol "LDPE" on them.
Type 5: Polypropylene - Safe
Polypropylene containers do not leach harmful chemicals into foods or liquids. They commonly contain yogurt, medicine, drinks, ketchup and medicines. Type 5 plastic is flexible, hard and semi-transparent and has high resistance to solvents. Polypropylene containers may have the symbol "PP" on them.
Type 7: Polycarbonate
You should avoid type 7 plastic containers because they may contain bisphenol A that leaches into their contents. Type 7 plastics often have the symbol "PC" or "Other" on them. You will find polycarbonate plastics in 3- and 5-gallon water-cooler bottles; hard, plastic reusable water bottles; and to-go coffee mugs. Manufacturers use polycarbonate for these purposes because it is virtually shatter-proof.