Heart Health
Why Is My Blood Pressure High?
A simple guide to the body systems, lifestyle factors, and medical conditions that can raise blood pressure.
Patient information page | Last reviewed: June 2026
The quick answer
High blood pressure is usually not caused by one thing. It often develops from a mix of ageing, family history, salt and water balance, blood vessel stiffness, body hormones, sleep, stress, weight, activity levels, medicines, and other health conditions. Many people feel normal, but treatment matters because high blood pressure can strain the heart, brain, kidneys, eyes, and blood vessels over time.
- What it means
- Why it rises
- Salt and kidneys
- Blood vessels
- Hormones and stress
- Lifestyle factors
- Medical causes
- Urgent help
What does high blood pressure mean?
Blood pressure is the force of blood pushing against the walls of the arteries. Arteries are the blood vessels that carry blood from the heart to the rest of the body.
High blood pressure means this force is higher than is healthy over time. A single high reading does not always mean you have long-term high blood pressure, but repeated high readings should be checked and discussed with a doctor.
Blood pressure depends mainly on how much blood the heart is pumping and how tight, narrow, or stiff the blood vessels are.
Why does blood pressure become high?
For most people, there is no single cause. High blood pressure usually develops slowly over many years because of a mix of body chemistry, ageing, family history, lifestyle, and other health conditions.
Primary hypertension
This is the most common pattern. There is no one clear cause. Blood pressure rises because several risk factors and body systems act together.
Secondary hypertension
This means high blood pressure is caused or strongly driven by another condition, medicine, hormone problem, kidney problem, pregnancy-related condition, or stimulant.
Salt, water balance, and the kidneys
The kidneys play a major role in blood pressure. They help control how much salt and water stays in the body.
If the body holds on to too much salt, it also holds on to more water. This can increase the amount of fluid in the bloodstream and raise blood pressure.
Some people are more sensitive to salt than others. For them, even a moderate amount of salt can affect blood pressure. Reducing salt can help many people, especially when most salt is coming from processed foods, packaged snacks, restaurant meals, pickles, sauces, or salted ready-made foods.
Tight or stiff blood vessels
Blood vessels are not just pipes. They can relax or tighten.
When blood vessels tighten, blood pressure rises. When blood vessels relax, blood pressure falls.
Over time, blood vessels can become stiffer because of ageing, diabetes, kidney disease, smoking, high cholesterol, inflammation, or long-standing high blood pressure itself. Stiffer arteries can make the top blood pressure number rise.
Body hormones and stress signals
The body has hormone systems that control blood pressure. One important system tells the kidneys to hold on to salt and water and tells blood vessels to tighten. This is useful in dehydration or blood loss, but if it stays overactive, blood pressure can remain high.
The nervous system can also raise blood pressure. Pain, poor sleep, anxiety, stress, stimulants, and some medical conditions can increase the body’s fight-or-flight signals. This can make the heart beat faster and the blood vessels tighten.
Lifestyle factors that can raise blood pressure
Blood pressure can be affected by daily habits, but these factors do not affect everyone equally. Some people have high blood pressure despite a healthy lifestyle. Others develop it mainly because of lifestyle and weight-related factors.
- Too much salt: especially from processed, packaged, restaurant, or heavily salted foods.
- Being above a healthy weight for your body: this can increase the workload on the heart and affect hormones that control blood pressure.
- Low physical activity: regular movement helps blood vessels work better and supports weight, insulin, and heart health.
- Alcohol: drinking too much alcohol can raise blood pressure and make medicines work less well.
- Smoking and nicotine products: these can tighten blood vessels and increase strain on the heart and arteries.
- Poor sleep: short sleep, broken sleep, and obstructive sleep apnoea can contribute to high blood pressure.
- Long-term stress: stress does not explain every case, but it can worsen blood pressure through sleep, hormones, alcohol, smoking, food choices, and nervous system activation.
- Low intake of fruit, vegetables, pulses, nuts, seeds, and other potassium-rich foods: these foods can support blood pressure control as part of an overall healthy diet.
Important note about potassium
Potassium-rich foods are helpful for many people, but potassium supplements and potassium-based salt substitutes are not safe for everyone. If you have kidney disease, take medicines that affect potassium, or have been told your potassium is high, ask your doctor before increasing potassium supplements or using salt substitutes.
Medical causes of high blood pressure
Sometimes high blood pressure is caused by another condition. This is called secondary hypertension. A doctor may look for these causes if blood pressure is very high, starts at a young age, is difficult to control, or appears suddenly.
Examples of secondary causes
| Cause | How it may raise blood pressure | When a doctor may suspect it |
|---|---|---|
| Kidney disease | The kidneys may not control salt, water, and blood vessel hormones normally. | Abnormal urine tests, abnormal kidney blood tests, swelling, diabetes, or known kidney problems. |
| Narrowing of the blood vessels to the kidneys | The kidney may behave as if the body has low blood flow and activate pressure-raising hormones. | Sudden worsening, difficult-to-control readings, or kidney function changes after some blood pressure medicines. |
| Hormone problems | Conditions affecting aldosterone, thyroid hormones, adrenal hormones, or other systems can raise blood pressure. | Low potassium, palpitations, sweating attacks, weight changes, tremor, or unusual patterns of blood pressure. |
| Obstructive sleep apnoea | Repeated drops in oxygen and broken sleep can activate stress signals and raise blood pressure. | Loud snoring, witnessed pauses in breathing, daytime sleepiness, morning headaches, or resistant hypertension. |
| Medicines and stimulants | Some substances can retain salt and water, tighten blood vessels, or stimulate the nervous system. | New or worsening high readings after starting anti-inflammatory painkillers, steroid tablets, decongestants, some contraceptive pills, some antidepressants, recreational drugs, or stimulants. |
| Pregnancy-related high blood pressure | Pregnancy can cause specific blood pressure conditions that need prompt medical assessment. | High readings during pregnancy or after delivery, especially with headache, visual symptoms, swelling, tummy pain, or feeling very unwell. |
Why do I feel normal if my blood pressure is high?
High blood pressure often causes no symptoms. Many people feel completely well.
This is why checking blood pressure matters. Even without symptoms, high blood pressure can slowly strain the heart, brain, kidneys, eyes, and blood vessels over time.
The aim of treatment is not just to improve a number. It is to reduce the risk of heart attack, stroke, kidney disease, heart failure, vision problems, and other complications in the future.
A high reading is not always a diagnosis
Blood pressure can rise temporarily because of pain, stress, exercise, caffeine, a full bladder, poor sleep, or anxiety during a clinic visit. If readings are high but you feel well, your doctor may ask for repeated clinic readings, home readings, or 24-hour monitoring before confirming the diagnosis.
Can high blood pressure improve?
Yes. In many people, blood pressure can improve with lifestyle changes, medicines, or both.
-
Reduce salt. Start with processed and packaged foods, salty snacks, pickles, sauces, restaurant meals, and added salt at the table.
-
Eat more whole foods. A pattern with vegetables, fruit, pulses, whole grains, nuts, seeds, and less highly processed food can support blood pressure control.
-
Move regularly. Walking, cycling, swimming, resistance training, or other regular activity can help, as long as it is suitable for your health and fitness level.
-
Address weight, sleep, alcohol, and smoking. These can all affect blood pressure, but the best plan depends on the person.
-
Take prescribed medicines regularly. Some people need medicine even with a healthy lifestyle. This usually means the body needs extra help to control blood pressure safely.
When to seek urgent help
Seek emergency medical help if a very high blood pressure reading is associated with chest pain, severe breathlessness, weakness or numbness on one side of the body, facial drooping, difficulty speaking, new confusion, fainting, severe headache with neurological symptoms, vision loss, seizure, or severe symptoms in pregnancy. If a reading is around 180/120 mmHg or higher, repeat it after a few minutes of rest. If it remains very high and you have serious symptoms, seek emergency medical help immediately.
Key message
High blood pressure is usually caused by a mix of factors. The main mechanisms are extra salt and water retention, tighter or stiffer blood vessels, overactive hormone and stress systems, ageing, genetics, and sometimes other medical conditions.
You may feel completely normal, but treating high blood pressure is important because it protects your heart, brain, kidneys, eyes, and blood vessels over the long term.