You may not be familiar with the term thermal paper, but actually you often come across it in your daily life in the form of cash-register receipts.

Thermal papers used in cash registers have a chemical coating which turns black in areas where it is heated to produce an image. Thermal printing is broadly used to produce cash-register receipts in supermarkets, restaurants and ATM counters as well as Mark Six printed tickets, luggage tags and boarding passes. Different studies have found that the chemical coating on thermal paper contains bisphenol A (BPA), a chemical which can be absorbed through the skin. Researchers have raised concerns over BPA's potential to cause adverse health effects; should we avoid touching cash-register receipts in order to safeguard our health?

Professor Chris Wong of the Department of Biology points out that most cash-register receipts contain BPA. In 2015, the European Food Safety Authority (EFSA) set the tolerable daily intake for BPA at four micrograms per kilogram of body weight per day. "There are differing views on the impact of BPA on human health, for example, some animal experimental studies have shown that BPA could disrupt the proper functioning of hormones and lead to obesity. Other studies have pointed out that BPA can adversely affect blood pressure, nervous system, functioning of liver, kidney and pancreas as well as behaviour. Excessive intake of BPA may even raise the risk of breast and prostate cancers. However, there is no strong evidence of the direct impact of BPA on human health so BPA may not be the single reason for the above health risks. The jury is still out on just how harmful BPA is."

Professor Wong adds that since BPA is rapidly metabolised by the human body and excreted through urine, it is believed that exposure to low doses of BPA through limited skin contact with thermal papers would not cause adverse effects on humans.

Despite the fact that thermal papers may not be that "harmful", Professor Wong suggests pregnant women and infants to avoid exposure to BPA because they face a higher risk than normal adults. If someone is worried about the possible harmful effect of contacting thermal papers, they are suggested to wash their hands after touching receipts, and cashiers and salesmen can wear gloves while working. "In fact, BPA is found on many everyday items, not just thermal paper. For example, it is used to line food cans to prevent corrosion. Apart from paying attention to BPA exposure through skin, we should also take note of BPA ingested orally and avoid using food and beverage containers with BPA."