Thermal paper is an ubiquitous material in modern commerce, used for printing receipts, tickets, and labels. The question of whether this paper contains Bisphenol A (BPA) stems from the chemical’s widespread use in the heat-sensitive coating that makes thermal printing possible. BPA has been a standard component in this paper type for decades, leading to concerns about consumer exposure. Since the chemical is not chemically bound within the paper, it is available for transfer upon contact, igniting a public health debate regarding its safety.
Why Bisphenol A is Used in Thermal Paper
Thermal paper functions through a chemical reaction triggered by heat. The paper is coated with a mixture containing two primary components: a colorless dye (often a leuco dye) and a developer. When the thermal printer head applies heat, the dye and the developer melt and mix.
Bisphenol A acts as the color developer, a slightly acidic substance that reacts with the colorless dye. This reaction causes the dye to change its chemical structure, resulting in the visible image or text. BPA was favored for this application because it is effective, stable, and inexpensive to use in manufacturing.
The presence of BPA in this coating is significant because it is in a “free” or unbound form, making it a potential source of human exposure. Concentrations often range from 8 to 17 grams per kilogram of paper (0.9% to 2.1% by weight). This concentration ensures the quick and clear development of the printed image.
Skin Absorption and Rates of Transfer
Handling thermal paper provides a direct route for BPA to enter the body through the skin, a process known as dermal absorption. When a person touches a receipt, BPA transfers from the paper’s surface onto the skin. Studies show that a brief, five-second hold of a thermal receipt can transfer approximately 1 microgram of BPA if the skin is dry.
The rate of transfer increases significantly when the skin is wet or coated with substances like hand sanitizer, lotions, or oils. The presence of alcohol in hand sanitizer acts as a solvent, which can increase the amount of BPA transferred to the skin by as much as ten times. Once the chemical transfers to the skin, it can penetrate the dermal layer.
Experiments have shown that BPA transferred from thermal paper remains extractable from the skin for up to two hours, indicating deep penetration. This exposure is particularly relevant for workers, such as cashiers, who repeatedly handle thermal paper, potentially reaching an exposure of up to 71 micrograms per day. Research suggests up to 25% of the BPA applied to the skin can be absorbed over 24 hours.
Understanding the Health Effects of BPA
The concern over dermal exposure to BPA is rooted in its classification as an endocrine-disrupting chemical (EDC). EDCs are synthetic compounds that interfere with the body’s hormonal systems, which control growth, development, and biological processes. BPA’s chemical structure allows it to mimic the natural hormone estrogen.
By binding to estrogen receptors, BPA can disrupt the signaling pathways that hormones regulate. This hormonal interference has been linked to impacts on reproductive health, including impaired fertility and Polycystic Ovary Syndrome (PCOS). Exposure is also associated with developmental issues and neurobehavioral problems, such as anxiety and depression.
BPA exposure is implicated in metabolic dysfunction, including links to obesity and insulin resistance. Cardiovascular concerns, such as hypertension and heart disease, have been associated with the chemical. The BPA absorbed contributes to the overall body burden, which is a public health concern given the ubiquity of exposure sources.
The Shift to BPA-Free Options
In response to public and regulatory pressure, the thermal paper industry began transitioning away from BPA, leading to the widespread adoption of “BPA-free” thermal paper. However, the most common replacement chemical used as the color developer is Bisphenol S (BPS), which is structurally similar to BPA.
Using BPS is an example of “regrettable substitution,” as research indicates that BPS also exhibits endocrine-disrupting properties. Studies suggest that BPS may carry many of the same health risks as BPA, including effects on reproductive and metabolic systems. Therefore, a product labeled “BPA-free” often contains BPS or another similar bisphenol compound.
Truly safer alternatives are emerging in the form of “phenol-free” thermal paper, which utilizes non-phenolic developers, such as those based on vitamin C or urea compounds. Consumers can minimize exposure by declining printed receipts or storing them separately from currency. Avoiding hand sanitizer immediately before or after handling thermal paper also helps reduce dermal absorption.