In most cases, it's not clear exactly what causes high blood pressure. But there are things that can increase your risk.

You might be more at risk if you:

• are overweight
• eat too much salt and do not eat enough fruit and vegetables
• do not do enough exercise
• drink too much alcohol or coffee (or other caffeine-based drinks)
• smoke
• have a lot of stress
• are over 65
• have a relative with high blood pressure
• are of black African or black Caribbean descent
• live in a deprived area

Making healthy lifestyle changes can sometimes help reduce your chances of getting high blood pressure and help lower your blood pressure if it's already high.

Find out more about how to prevent high blood pressure

In about 1 in 10 cases, high blood pressure happens as the result of an underlying health condition or taking a certain medicine.

Health conditions that can cause high blood pressure include:

• kidney disease
• diabetes
• long-term kidney infections
• sleep apnoea – where the walls of the throat relax and narrow during sleep, interrupting normal breathing
• glomerulonephritis – damage to the tiny filters inside the kidneys
• narrowing of the arteries supplying the kidneys
• hormone problems – such as an underactive thyroid, an overactive thyroid, Cushing's syndrome, acromegaly, increased levels of the hormone aldosterone (hyperaldosteronism), and phaeochromocytoma
• lupus – a condition in which the immune system attacks parts of the body, such as the skin, joints and organs
• scleroderma – a condition that causes thickened skin, and sometimes problems with organs and blood vessels

Medicines that can increase your blood pressure include:

• the contraceptive pill
• steroids
• non-steroidal anti-inflammatory drugs (NSAIDs) – such as ibuprofen, aspirin and naproxen
• some pharmacy cough and cold remedies
• some herbal remedies – particularly those containing liquorice
• some recreational drugs – such as cocaine and amphetamines
• some selective serotonin-noradrenaline reuptake inhibitor (SSNRI) antidepressants – such as venlafaxine

In these cases, your blood pressure may return to normal once you stop taking the medicine or drug.