We’ve mentioned several times already on this blog about bisphenol A (BPA) and how this endocrine disrupting chemical is present in all sorts of plastics from water bottles, baby bottles, and dental sealants. What may not be inherently obvious is where else BPA can be found in everyday products. One example is with thermal printing paper: were you aware that thermal printing paper contains BPA and once touched could possibly transfer onto your fingers?
Who Uses Thermal Paper?
Thermal paper is found in many places, though most commonly it is found in the receipt paper at a store, or the paper used in certain recorders in various laboratories. Could employees working the cash register or even the customer handling the receipt to file away in their records be exposed to BPA through the thermal paper? Could researchers working with recorders be exposed to BPA when handling the paper to analyze their results?
What exactly IS thermal paper?
I already mentioned that thermal paper is the paper that’s used often in cash registers as well as recorders in the laboratory. Breaking it down even further, imagine a piece of thermal cash register paper. On the side to be printed, there is a layer of printing ink covering the entire surface. The color used to print contains a leuco dye, which is a chemical that can exist in two forms: a colored form and a colorless form. When it comes time to print, the thermal head of the printer causes the leuco dye and other chemicals on the surface to melt and react with one another, which results in the dye taking on its dark colored form. These chemicals, in combination with the heating and melting process, result in chemical products including the endocrine disruptor, BPA.
Could the BPA on the thermal paper transfer to our skin?
This is certainly an interesting question, and one that has not been studied too often. Those few studies in animals examining absorption of BPA by the skin found that BPA can be absorbed by the udders of cows, as well as through pig skin. What about humans? Is handling this thermal paper on our receipts a cause for concern? Can the BPA on this paper be absorbed through our skin as it has been shown to occur in cows and pigs?
In a study by a team of researchers from the Official Food Control Authority of the Canton of Zürich in Switzerland, they examined whether or not BPA can be transferred from thermal paper to the skin, and if there are certain conditions that are better or worse for this transfer than others. Several interesting results came out of this study.
First, holding thermal paper transferred on average 1.13ug of BPA onto the fingers. If the fingers were humid or greasy, then 10 times more BPA was transferred from the paper to the fingers (on average 23ug/finger). The greatest amount of BPA transferred onto the fingers was when the fingers were so wet that some of the particulates from the paper itself stuck on to the fingers.
Second, when touching the paper in multiple spots with “normal” (i.e. dry) skin, no more BPA was transferred that had been after the first initial touch. Basically, this means that having regular contact with this type of paper throughout the day results in a mostly consistent level of BPA on the fingers the entire day. If all 10 fingers were in contact with the paper, then on average 11ug of BPA would be transferred onto the skin. If the paper is crumpled up, theoretically a greater surface area could touch the fingers and thus more BPA could be absorbed (not tested).
Wash those hands!
What happens if you immediately wash your hands after coming in contact with BPA-laden thermal paper? The Swiss researchers took a look at this as well, and found that immediately washing ones hands after coming into contact with the thermal paper was very helpful in reducing BPA levels on the skin. Somewhere around 90% of the BPA was washed away when the hands were immediately washed, but it’s important to note that some of the BPA still remained and was unable to be washed off, perhaps due to its absorbance too deep into the skin.
It was noted that if the hands were wet, for example when the BPA was applied in this experiment using ethanol, a significant increase in absorption of BPA into the skin was observed. So much so, that after 1 hour, it was already absorbed into the skin and it could not be washed away. If the fingers were completely dry prior to touching the thermal paper, it was found that most of the BPA could still be washed away, even at 2 hours. Though a lot could be washed away, it is important to note that 2 hours after thermal paper contact with dry skin, 27% of the BPA could NOT be washed off and was already absorbed by the skin.
How much BPA in a day?
Based on the results of this paper, you can calculate just how much BPA would be absorbed into your skin if you were say working the register at a busy store, or maybe taking a lot of readings and doing a lot of analysis on your laboratory recorder. Luckily for me, the Swiss researchers already did this math, so I don’t have to.
Let’s say you work the cash register at a store for a 10 hour shift. Based on the results of this preliminary study, each one of your fingers should absorb about 0.09ug of BPA per hour. Let’s say you touch the thermal paper enough so that you maintain about 3ug of BPA on your fingertips throughout the day. Assuming your washing your hands periodically throughout the day, your skin would absorb roughly 41ug of BPA. If you don't wash your hands at all, even more BPA would be absorbed into your skin, resulting in a worst-case scenario of 71ug of BPA that day. Note: if you were wearing lotion or your hands were somehow frequently wet (perhaps you like your fingers to help grab at the paper), the results of this study would indicate that even more BPA could be absorbed, perhaps by a factor of 10!
How to avoid BPA exposure via thermal paper?
Well, the results of this study would indicate that washing your hands frequently should remove a significant amount of the BPA transferred onto your fingers from the thermal paper. Also, try not to wear any hand lotions, creams, or anything else that might give your hands extra moisture, as this moisture seems to act as a vector for even more BPA to be quickly absorbed into your body.
Think about it-> if you spill some liquid on the floor and try to clean it up with a bone dry sponge, it takes forever for the liquid to be absorbed into the porous material. On the other hand, if you dampened the sponge prior to cleaning up the mess, you’ll notice the liquid is much more readily absorbed into the sponge and you have the surface cleaned in no time!
Something similar is likely happening with your skin: Dry skin = Very little BPA absorption. Damp skin = you may as well install a BPA IV into your veins (well, OK, not THAT much, but it’ll get absorbed real fast).
The next step in this research would be to determine if the levels of BPA absorbed actually cause any damage to the person that is handling the thermal paper. Are the levels of BPA absorbed by the skin enough to cause harm? Technically, the levels observed are actually lower than the allowed amount by US and European entities, however, many studies have shown that there can be significant “low dose effects” of BPA at levels much lower than allowed.
In the meantime, wash your hands, and don’t slather yourself with lotion if you’re going to be working with thermal paper all day.
Source: Biedermann, S., Tschudin, P., Grob, K. 2010. Transfer of bisphenol A from thermal paper tothe skin. Analytical and Bioanalytical Chemistry 398: 571-576.