Systolic BP lower than 90 mm Hg or diastolic BP lower than 60 mm Hg is considered low blood pressure or hypotension. Unlike hypertension, hypotension is more likely to be due to a primary cause (dehydration, heart disease, drugs, endocrine disease, etc.) and thus therapy is often aimed at treating the primary cause. Borderline BP with no obvious cause can be treated with increased salt and water intake, regular mild exercises, cutting down on alcohol, etc.). Drug therapy can be used if such hypotension is not amenable to these measures.
^ Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents, National Heart, Lung, and Blood Institute (Dec 2011). "Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents: summary report". Pediatrics. 128 Suppl 5: S213–56. doi:10.1542/peds.2009-2107C. PMC 4536582. PMID 22084329.
For a manual monitor, you have to hold the pressure gauge in one hand (your weaker hand) and the bulb in the other hand. Inflate the cuff until it reads about 30 points above your normal systolic pressure. At this point, you should not hear your pulse in the stethoscope. When you hear the first heart beat, this is the systolic pressure. As you deflate the cuff, keep listening for a heart beat. When you can no longer hear it, that is your diastolic pressure.
The first chemical for hypertension, sodium thiocyanate, was used in 1900 but had many side effects and was unpopular.[152] Several other agents were developed after the Second World War, the most popular and reasonably effective of which were tetramethylammonium chloride, hexamethonium, hydralazine, and reserpine (derived from the medicinal plant Rauwolfia serpentina). None of these were well tolerated.[159][160] A major breakthrough was achieved with the discovery of the first well-tolerated orally available agents. The first was chlorothiazide, the first thiazide diuretic and developed from the antibiotic sulfanilamide, which became available in 1958.[152][161] Subsequently, beta blockers, calcium channel blockers, angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers, and renin inhibitors were developed as antihypertensive agents.[158]
Health care providers measure blood pressure with a sphygmomanometer (sfig-mo-muh-NAH-muh-ter), which has a cuff that's wrapped around the upper arm and pumped up to create pressure. When the cuff is inflated, it squeezes a large artery in the arm, stopping the blood flow for a moment. Blood pressure is measured as air is gradually let out of the cuff, which allows blood to flow through the artery again.
A hypertensive emergency, unlike the similar sounding hypertensive urgency, is characterized by serious, life-threatening complications. A hypertensive emergency means that the blood pressure is >180 mm Hg or the diastolic pressure is >120 mm Hg, and that end-organ damage is occurring. Signs and symptoms can include shortness of breath, anxiety, chest pain, irregular heart rate, confusion, or fainting. 
We tend not to think about our blood pressure — it’s a normal function of our heart working regularly. However, when blood pressure stays high over an extended period it means the heart is working harder than it should. Since hypertension usually doesn’t have symptoms, we don’t know what is happening unless we measure it. Accurately measuring blood pressure provides a glimpse into what’s happening inside our bodies without needing expensive diagnostic tests.
Facial flushing: Facial flushing occurs when blood vessels in the face dilate. It can occur unpredictably or in response to certain triggers such as sun exposure, cold weather, spicy foods, wind, hot drinks and skin-care products. Facial flushing can also occur with emotional stress, exposure to heat or hot water, alcohol consumption and exercise — all of which can raise blood pressure temporarily. While facial flushing may occur while your blood pressure is higher than usual, high blood pressure is not the cause of facial flushing.  
Generally, blood pressure tends to be higher if more blood is pumped into the arteries or if the arterioles are narrow and/or stiff. Narrow and/or stiff arterioles, by resisting the flow of blood, increase blood pressure. Arterioles may become narrower when the muscles surrounding them contract. Arterioles may become stiff and narrow when older patients develop atherosclerosis.
If your blood pressure is always on the low side and you do not have any of the above symptoms, there is usually no cause for concern. Similarly, if you have a single at-home blood pressure reading that is abnormally low without any symptoms, you probably do not need to see your doctor. It is normal for your blood pressure to rise and fall over time, and your body is usually able to get your blood pressure back to normal.
Much of the disease burden of high blood pressure is experienced by people who are not labeled as hypertensive.[87] Consequently, population strategies are required to reduce the consequences of high blood pressure and reduce the need for antihypertensive medications. Lifestyle changes are recommended to lower blood pressure, before starting medications. The 2004 British Hypertension Society guidelines[87] proposed lifestyle changes consistent with those outlined by the US National High BP Education Program in 2002[95] for the primary prevention of hypertension:
Many mechanisms have been proposed to account for the rise in peripheral resistance in hypertension. Most evidence implicates either disturbances in the kidneys' salt and water handling (particularly abnormalities in the intrarenal renin–angiotensin system)[61] or abnormalities of the sympathetic nervous system.[62] These mechanisms are not mutually exclusive and it is likely that both contribute to some extent in most cases of essential hypertension. It has also been suggested that endothelial dysfunction and vascular inflammation may also contribute to increased peripheral resistance and vascular damage in hypertension.[63][64] Interleukin 17 has garnered interest for its role in increasing the production of several other immune system chemical signals thought to be involved in hypertension such as tumor necrosis factor alpha, interleukin 1, interleukin 6, and interleukin 8.[65]
Quitting smoking. Visit Smoking and Your Heart and the National Heart, Lung, and Blood Institute’s Your Guide to a Healthy Heart [PDF – 2MB]. Although these resources focus on heart health, they include basic information about how to quit smoking. For free help and support to quit smoking, you can call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
tilt table test – usually recommended if your doctor suspects you might have orthostatic hypotension or NMH (During this diagnostic test, a person lies on a table and then the table is tilted to raise the upper part of their body. This simulates the change in position from sitting or lying down to standing up. People with orthostatic hypotension or NMH may feel dizzy, lightheaded, or even faint when their position changes.)
In Europe hypertension occurs in about 30-45% of people as of 2013.[12] In 1995 it was estimated that 43 million people (24% of the population) in the United States had hypertension or were taking antihypertensive medication.[141] By 2004 this had increased to 29%[142][143] and further to 32% (76 million US adults) by 2017.[7] In 2017, with the change in definitions for hypertension, 46% of people in the United States are affected.[7] African-American adults in the United States have among the highest rates of hypertension in the world at 44%.[144] It is also more common in Filipino Americans and less common in US whites and Mexican Americans.[6][145] Differences in hypertension rates are multifactorial and under study.[146]
In people aged 18 years or older hypertension is defined as either a systolic or a diastolic blood pressure measurement consistently higher than an accepted normal value (this is above 129 or 139 mmHg systolic, 89 mmHg diastolic depending on the guideline).[5][7] Other thresholds are used (135 mmHg systolic or 85 mmHg diastolic) if measurements are derived from 24-hour ambulatory or home monitoring.[79] Recent international hypertension guidelines have also created categories below the hypertensive range to indicate a continuum of risk with higher blood pressures in the normal range. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC7) published in 2003[27] uses the term prehypertension for blood pressure in the range 120–139 mmHg systolic or 80–89 mmHg diastolic, while European Society of Hypertension Guidelines (2007)[86] and British Hypertension Society (BHS) IV (2004)[87] use optimal, normal and high normal categories to subdivide pressures below 140 mmHg systolic and 90 mmHg diastolic. Hypertension is also sub-classified: JNC7 distinguishes hypertension stage I, hypertension stage II, and isolated systolic hypertension. Isolated systolic hypertension refers to elevated systolic pressure with normal diastolic pressure and is common in the elderly.[27] The ESH-ESC Guidelines (2007)[86] and BHS IV (2004)[87] additionally define a third stage (stage III hypertension) for people with systolic blood pressure exceeding 179 mmHg or a diastolic pressure over 109 mmHg. Hypertension is classified as "resistant" if medications do not reduce blood pressure to normal levels.[27] In November 2017, the American Heart Association and American College of Cardiology published a joint guideline which updates the recommendations of the JNC7 report.[88]
Being overweight increases the risk of getting hypertension and increases the workload required of your heart. Diets designed to control blood pressure are often designed to reduce calories as well. Most of these diets require decreasing consumption of fatty foods and sugars while increasing your intake of lean protein, fiber, fruits, and vegetables. A weight loss of just 10 pounds can make a significant difference in your blood pressure.
6. Cultivate stress management. You don’t need a meta-analysis of cohort studies to prove stress can raise blood pressure, but they exist. You can’t eliminate stress, but you can minimize its impact. Research shows yoga and meditation create effective strategies to manage stress and blood pressure. If those aren’t your thing, consider other stress-relieving tactics including deep breathing or practicing mindfulness.
The American Heart Association, or AHA, explains that the early symptoms of high blood pressure that people tend to think about are largely mythical. You are unlikely to notice “classic” signs such as anxiety, insomnia, or flushing in your face. You could have blood spots in your eyes due to subconjunctival hemorrhage, but dizziness itself is not among the essential symptoms of high blood pressure.
NHLBI Expert Panel on Cardiovascular Health and Risk Reduction in Children and Adolescents. We have supported the development of guidelines based on up-to-date research to evaluate and manage risk of heart disease in children and adolescents, including high blood pressure. Visit Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents for more information.
A blood pressure reading contains two numbers: systolic pressure and diastolic pressure. Systolic pressure is the top or first number in your blood pressure reading; it indicates the pressure within your arteries when your heart pumps out blood. Diastolic pressure is the bottom number, and shows the pressure in your arteries while your heart is filling with blood.

An exception to this is those with very high blood pressure readings especially when there is poor organ function.[79] Initial assessment of the hypertensive people should include a complete history and physical examination. With the availability of 24-hour ambulatory blood pressure monitors and home blood pressure machines, the importance of not wrongly diagnosing those who have white coat hypertension has led to a change in protocols. In the United Kingdom, current best practice is to follow up a single raised clinic reading with ambulatory measurement, or less ideally with home blood pressure monitoring over the course of 7 days.[79] The United States Preventive Services Task Force also recommends getting measurements outside of the healthcare environment.[80] Pseudohypertension in the elderly or noncompressibility artery syndrome may also require consideration. This condition is believed to be due to calcification of the arteries resulting in abnormally high blood pressure readings with a blood pressure cuff while intra arterial measurements of blood pressure are normal.[81] Orthostatic hypertension is when blood pressure increases upon standing.[82] 

Hypertension clinical guidelines from the American Heart Association are comprehensive guidelines for healthcare professionals for the detection and treatment of high blood pressure in a wide range of patients. Included in the 2018 hypertension clinical guidelines are proper methods for measuring blood pressure, risk factors for hypertension, and hypertension treatment for different populations.
Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure symptoms tend to be more upfront and easily recognizable. The development of symptoms is often a warning sign of a potentially serious underlying disorder. Generally speaking, your blood pressure would need to fall pretty dramatically before symptoms develop.