A pioneering new technology is promising to make diagnosing high blood pressure as easy as taking a selfie. But there’s a catch – it might not work on people of colour.

At the moment, the only way to measure blood pressure is to have a cuff-based blood pressure test. This week Kang Lee, from the University of Toronto, and his team published proof-of-concept that a smartphone app taking a short video can accurately detect blood pressure.

Using something called “transdermal optical imaging”, it could measure your blood pressure using your smartphone by analysing facial blood flow changes filmed on a smartphone camera, then using advanced machine learning and computer modelling to give a blood pressure value.

But the majority of participants of this study (over 95%) were of East Asian or European descent, so there’s a big question mark about whether the results of this paper can be extended to people with darker skin.

In an article for Quartz, Katherine Ellen Foley wrote the validity of the study “is still in question for people with darker skin.”

She explained: “Another protein found in skin is melanin, which is responsible for skin tone. The smartphone app should be able to tell the difference between light bouncing off melanin and light bouncing off hemoglobin. But without representative testing on individuals with darker skin tones, it’s impossible to say whether it actually can measure blood pressure with the same degree of accuracy.”

According to Public Health England, people from Black African and Black Caribbean ethnic groups have a higher risk of hypertension than the general population.

Racial bias in artificial intelligence is nothing new. A 2017 paper in Science found that an A.I. studying English began to discriminate against African-American names, and associated them with unpleasant terms when compared to European-American names.

The blood pressure researchers from Toronto recognise this issue, and plan to recruit a more diverse range of participants for the development stage. If they don’t they run the risk of the technology being ineffective to some of the people who need it most.

Approximately 1 in 4 adults worldwide have high blood pressure, and many of them don’t realise. According to the Global Burden of Disease in 2015, high blood pressure was responsible for 10.7 million deaths worldwide.

High blood pressure (or hypertension) is the third biggest risk factor for disease in the UK, after smoking and a poor diet. It increases the risk of heart failure, stroke and coronary heart disease.

It is also hard to diagnose due to a lack of symptoms, which has led to it being labelled a ‘silent killer’.