You’ve probably noticed them as you go about your daily life. Seeing red-faced, overweight, sweaty, stressed out strangers in the street perhaps makes you worry about their blood pressure, and even help inspire you to go to the gym more often. If they are friends or colleagues and they start complaining about headaches and nosebleeds, you might fear that a heart attack or stroke can’t be far away. But is it really possible to tell who has high blood pressure simply by looking at them?

Our faces flush when blood vessels just beneath the skin on our faces dilate to allow small increases in blood flow. Blushing can take two forms. There’s the sudden kind where your face unexpectedly feels hot, perhaps because of shame or embarrassment, and then there is the more gradual blush that can take as long as 20 minutes to reach its peak – this can also be a sign of embarrassment, or be caused by things like extreme temperatures and hard exercise. Both are accompanied by a temporary rise in blood pressure, but facial reddening caused by cycling up a hill, going for a walk on a cold day or bumping into an ex-partner doesn’t indicate long-term, problematic hypertension.

If facial redness is persistent, it can indicate rosacea, a skin condition where the small blood vessels can become chronically inflamed. High blood pressure can exacerbate it, but someone with rosacea does not necessarily have high blood pressure.

Ecrine glands, which secrete sweat, exist in especially large concentrations in the face, along with the hands, feet and armpits. They are controlled by the sympathetic nervous system, whose job it is to control our body’s fight or flight responses when we detect dangers. Excessive sweating, known as hyperhidrosis, can be genetic or a symptom of various other conditions, but isn’t a sign of hypertension.

Stressful events don’t always have to be life-threatening for them to stimulate our fight or flight responses. Missing the bus when you’re late or having an argument with a friend will set the heart racing and make your blood pressure rise. Once we’ve found another way home or made up, these vital signs will rapidly return to normal. The relationship between stress and high blood pressure is complex, and if a person experiences repeated spikes in blood pressure because of very stressful situations, this can contribute to hypertension. But someone who gets angry now and then doesn’t necessarily have high blood pressure.

In the head?

But how about those tension headaches? Doctors used to think that they were caused by hypertension, but now the evidence suggests the opposite is true. When you have your blood pressure taken, there are two readings. The higher number is the systolic blood pressure – the pressure in the arteries when the heart muscles contract. Researchers found that people with higher systolic blood pressure were much less likely to get headaches than those with lower readings. Those with larger differences between the two readings – called pulse pressure - also had fewer headaches. A Brazilian study also confirmed that people with high blood pressure are less likely to get migraines.

Curiously, drugs that reduce blood pressure are sometimes used as an effective treatment for migraines, presenting us with something of a paradox. One hypothesis is that the reason the pain is reduced is not due to the drop in blood pressure, but to other effects of the medication. And it’s not just headaches and migraines. A recent Norwegian study followed more than 17,000 people over several years to see how many developed back pain. A third of the sample did, but again, the higher their systolic and pulse pressure, the less likely they were to do so.

This decreased sensitivity to pain as a result of high blood pressure is called hypertension-associated hypalgesia. It also explains why some women find their migraines disappear during the later stages of pregnancy, when their blood pressure naturally rises. No one is entirely sure why this happens, but one theory is that the stiffening of the blood vessels caused by high pressure stops the nerve endings working properly, and as a result the pain is dulled.

This doesn’t mean hypertension is a good thing, but it does suggest that some symptoms, including headaches, can be an indication of normal rather than high blood pressure.

If headaches aren’t a clue to high blood pressure, how about nosebleeds? Studies on the subject have had contradictory results. Austrian researchers, for example, found that patients arriving in emergency department of Vienna General Hospital with unstoppable nosebleeds did have higher blood pressure than other patients. However a Brazilian study found no association.

But these studies only looked at the people with nosebleeds. If we really want to know whether nosebleeds are a clue to high blood pressure we need to know how often patients with hypertension experience them. In a study in Greece of people going into hospital for high-blood-pressure emergencies only 17% had persistent nosebleeds. It seems that for some patients nosebleeds can provide a clue that their blood pressure might be elevated, but for most people it doesn’t.

So the simple answer is that high blood pressure is a largely symptomless condition, with one important caveat. If a person’s blood pressure suddenly reaches dangerously high levels, they are likely to experience severe anxiety, shortness of breath, excruciating headaches and dizziness. This can be a medical emergency and these symptoms shouldn’t be ignored.

But this happens only rarely. In 90% of cases the precise cause of hypertension is unknown. The only way to discover whether you have hypertension on an everyday basis is to have your blood pressure tested. So if seeing red-faced, sweaty, stressed friends or strangers makes you in any way smug about the state of your own arteries, just remember they don’t call high blood pressure the silent killer for nothing.

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