But as soon as they get home, their blood pressure returns to normal - although they have been diagnosed as hypertensive, and possibly given a prescription for a powerful antihypertensive drug.
Around 42 per cent of woman and 34 per cent of men have "white coat hypertension", researchers from the University of Barcelona in Spain have discovered. They assessed 69,045 hypertensive patients, and had them take their own blood pressure readings at home and over a 24-hour period - a technique known as ambulatory monitoring.
Only 63 per cent, on average, had true hypertension, measured as 140/90 (the first reading is the systolic, when the heart is beating, and the second is diastolic, when the heart is resting). Most of these were smokers, diabetics, or had heart problems. They also tended to be younger males.
(Source: Hypertension, 2011; doi: 10.1161/hypertensionaha.110.168948).