Explainer: Store receipts and BPA | Science News for Students

Explainer: Store receipts and BPA

A hormone-mimicking chemical can be found in paper copies of cash-register sales
Nov 22, 2017 — 6:30 am EST
credit card at register

Most credit-card and store receipts use thermal paper to print out a record of purchases. That paper may contain BPA, a chemical that can inappropriately fool the body into thinking it’s a hormone.


If you ever go shopping with scientists who study toxic chemicals, pay attention to what they do with a receipt. Some of them will stick that slip of paper into a zip-it-closed plastic baggie, not their pockets and wallets. Others will ask for a digital receipt. Why? It’s because there’s probably a chemical coating on that paper that contains bisphenol A, or BPA.

BPA is used for a host of different purposes. It is broadly used as a chemical building block of polycarbonate (Pah-lee-KAR-bo-nayt) plastics and of epoxy resins. Polycarbonates are hard, clear plastics that have an almost glasslike finish. They have been used to make water bottles, baby bottles, kitchen appliance bowls and more. The resins show up in a host of materials, including paints, adhesives and protective coatings — including clear coatings on the inside of food cans and on the outside of children’s teeth. BPA also ends up on some kinds of paper.

John C. Warner is a chemist. While working at Polaroid Corporation in the 1990s, he learned about the chemistry behind the papers now used for most receipts. These are known as thermal papers. To make some of them, manufacturers would coat a powdery layer of BPA onto one side of a piece of paper together with an invisible ink, Warner learned. “Later, when you applied pressure or heat, they would merge together and you’d get color.”

Warner thought little about such papers other than their design was clever. Until, that is, BPA exploded into the news in the early 2000s. At that point, he says, he began to have some doubts.

Research had begun showing that BPA could mimic the action of estrogen. That’s the primary female sex hormone in mammals and many other classes of animals. In the womb, studies found, BPA could disrupt the normal development of a rodent’s reproductive organs. And some animal studies found that BPA might even raise the risk of cancer.

This is a worry because BPA doesn’t stay locked inside the products that contain it. Studies showed that BPA can leach out of polycarbonate plastic. It also leaches out of can linings and into canned goods. It even had been found in the saliva of children whose teeth had been treated with a BPA-based resin (in hopes of limiting cavities).

pursed receipt
Many toxicologists now recommend that people carry receipts in something other than a wallet or purse — perhaps a plastic bag. That way any BPA won’t rub off and cross-contaminate money or other objects a person might handle.

By the early 2000s, Warner was teaching green chemistry at the University of Massachusetts in Boston and Lowell. “I'd send my students out to local stores to get their cash register receipts.” Back in the lab, they’d dissolve the paper. Then they’d run it through a mass spectrometer. This instrument could analyze the chemical composition of materials. A simple glance at its output would show whether there was a telltale spike signaling BPA.

And his students indeed found it, Warner says. Not in every receipt. But in plenty. Receipt papers that used BPA looked no different than ones that didn’t.

Paper can be a major source of BPA

Until at least 2009, neither the public nor the general science community had been aware of receipt papers as a potentially important source of exposure to BPA.

In many cases, Warner found, the amounts of it in paper were not trivial.

“When people talk about polycarbonate bottles, they talk about nanogram quantities of BPA [leaching out],” Warner observed back around 2009. A nanogram is a billionth of a gram. “The average cash register receipt that's out there and uses the BPA technology will have 60 to 100 milligrams of free BPA,” he reported several years back. That’s a million times more than what ends up in a bottle. (By free, he explained, it’s not bound into a polymer, like the BPA in a bottle. The individual molecules are loose and ready for uptake.)

As such, he argued, when it comes to BPA, for most people “the biggest exposures, in my opinion, will be these cash register receipts.”

Once on the fingers, BPA can be transferred to foods. A number of hormones — including estrogen — can be delivered through the skin by controlled-release patches. So, some scientists began to worry about whether BPA, too, might enter the skin.

In 2011, toxicologists showed it did. Two teams published data showing BPA could pass into the body through skin. Three years later, a team of university and government scientists showed that handling receipt paper could bring BPA into the body.

Paper companies started getting concerned. Before long, some began substituting other BPA relatives in their thermal-paper “inks.” Follow-up research would show, however, that some of these chemicals were as hormone-like as BPA was, at least in animal studies.

Several public-interest groups have been petitioning for companies to label any receipt papers that contain BPA (or one of its chemical cousins). That way, pregnant women would know to wash their hands after picking up a BPA-laced receipt. They would also know to keep it out of the hands of babies that might put fingers that handled such receipts into their mouths. 

Power Words

(more about Power Words)

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

bisphenol A (BPA)       A building block of polycarbonate plastics and many commercially important resins. This chemical gained widespread public attention when research showed it could mimic the activity of estrogen, a female sex hormone.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

development     (in biology) The growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.

digital     (in computer science and engineering)  An adjective indicating that something has been developed numerically on a computer or on some other electronic device, based on a binary system (where all numbers are displayed using a series of only zeros and ones).

disrupt     (n. disruption) To break apart something; interrupt the normal operation of something; or to throw the normal organization (or order) of something into disorder.

dissolve     To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

estrogen     The primary female sex hormone in most higher vertebrates, including mammals and birds. Early in development, it helps an organism develop the features typical of a female. Later, it helps a female’s body prepare to mate and reproduce.

green chemistry     A rapidly growing field of chemistry that seeks to develop products and processes that will pose little or no harm to living things or the environment.

hormone     (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polymer     A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

primary     An adjective meaning major, first or most important.

reproductive organs     The organs in a creature’s body that allows it to make and deliver eggs or sperm, and where appropriate, to nurture developing eggs and fetuses.

resin     A sticky, sometimes aromatic substance, often secreted by plants. It may also be the viscous starting ingredient for some plastics that will harden when heated or treated with light.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

rodent     A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

sex     An animal’s biological status, typically male or female. There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitals.

spectrometer     An instrument that measures a spectrum, such as light, energy, or atomic mass. Typically, chemists use these instruments to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

thermal     Of or relating to heat. (in meteorology) A relatively small-scale, rising air current produced when Earth’s surface is heated. Thermals are a common source of low level turbulence for aircraft.

toxicologist     A scientist who investigates the potential harm posed by physical agents in the environment. These may include materials to which we may be intentionally exposed, such as chemicals, cigarette smoke and foods, or materials to which we are exposed without choice, such as air and water pollutants. Toxicologists may study the risks such exposures cause, how they produce harm or how they move throughout the environment.

womb     Another name for the uterus, the organ in mammals in which a fetus grows and matures in preparation for birth.


Journal: S. Ehrlich, A.M. Calafat, O. Humblet. Handling of thermal receipts as a source of exposure to bisphenol A. Journal of the American Medical Association. Vol. 311, February 26, 2014, p. 859. doi: 10.1001/jama.2013.283735.

Journal: J.M. Braun et al. Variability and predictors of urinary bisphenol A concentrations during pregnancy. Environmental Health Perspectives. Vol. 119, January 2011, p. 131. doi: 10.1289/ehp.1002366. 

Journal: D. Zalko et al. Viable skin efficiently absorbs and metabolizes bisphenol A. Chemosphere. Vol. 82, January 2011, p. 424. doi: 10.1016/j.chemosphere.2010.09.058.