Improper use of thermal imaging systems designed to measure human body temperature could provide inaccurate readings, the US Food and Drug Administration (FDA) has warned.

The agency has issued several warning letters to firms offering unapproved, uncleared and unauthorised thermal imaging systems for sale.

The letters have been sent to Certify Global, Kogniz, Opgal Optronic Industries and Thermavis.

FDA chief medical officer William Maisel said: “While thermal imaging is not an effective diagnostic device for Covid-19, it can determine if someone has an elevated temperature, which can be an important risk management tool during the pandemic when used properly.

“But improper use and marketing of thermal imaging systems may lead to inaccurate temperature readings and pose a potential danger to public health. As part of the FDA’s ongoing commitment to transparency to the American public, the agency is providing important information to users about the correct use of these devices and is warning certain firms that the FDA will not tolerate their marketing of misbranded and adulterated products.”

Thermal imaging systems detect infrared light emitted from a person’s skin and convert that information into a temperature reading.

These systems are being used in many public spaces in the US as part of Covid-19 risk management to try and determine if someone has an elevated temperature.

Improper use of the devices can lead to inaccurate body temperature measurements, particularly when the systems are used to scan multiple individuals simultaneously.

The devices may incorrectly detect a normal body temperature when the person being measured actually has a fever, or incorrectly assess a person as having an elevated temperature when they do not.

The FDA said it may take further action on thermal imaging systems to protect consumers, and called for thermal imaging device issues to be reported to its MedWatch Voluntary Reporting Form.