Blood pressure rises when your heart pumps harder, your blood vessels tighten, or your body holds onto more fluid than usual. Sometimes all three happen at once. Normal blood pressure sits below 120/80 mmHg, and anything from 130/80 and above is now classified as hypertension under the latest 2025 guidelines from the American Heart Association.
The causes range from everyday triggers like stress and salt to underlying medical conditions you may not know you have. Understanding what drives your numbers up is the first step toward keeping them in check.
How Your Body Controls Blood Pressure
Your body runs a tightly regulated system to keep blood pressure stable. When pressure drops, your kidneys release an enzyme called renin, which kicks off a chain reaction. Renin converts a protein from your liver into a hormone that travels to your lungs and kidneys, where it gets converted again into its active form. This final hormone does two things: it tightens the muscular walls of your small arteries, and it signals your adrenal glands to release aldosterone, a hormone that tells your kidneys to hold onto sodium.
More sodium in your blood pulls in more water. More water means greater blood volume, and greater blood volume means higher pressure against your artery walls. This system is designed to be temporary, restoring pressure when it falls too low. Problems start when it stays activated longer than it should, or when outside factors keep pushing it into overdrive.
Salt and Fluid Retention
Eating too much sodium is one of the most common reasons blood pressure creeps up over time. The mechanism goes beyond simply holding onto extra water. High salt intake ramps up activity in your sympathetic nervous system (the “fight or flight” branch), resets the pressure-sensing mechanisms in your brain, and directly enhances the ability of your arteries to constrict. Over time, excess sodium also damages blood vessel linings, reduces their ability to relax, and promotes structural changes like wall thickening and narrowing of the vessel opening. All of these shifts increase resistance to blood flow and push pressure higher.
Stress, Adrenaline, and Acute Spikes
When you perceive a threat, whether it’s a near-miss in traffic or a tense conversation at work, your brain’s hypothalamus sends an alarm through your autonomic nervous system to the adrenal glands. They flood your bloodstream with adrenaline (epinephrine). Your heart beats faster and harder, key blood vessels constrict, and your blood pressure shoots up. This response is fast, typically peaking within seconds to minutes.
For most people, the spike is temporary. But chronic stress keeps this system partially activated for hours or days at a time, repeatedly elevating pressure and contributing to long-term damage to artery walls.
The Morning Surge
Blood pressure follows a daily rhythm, dipping to its lowest point during deep sleep and climbing as you approach waking. Several things converge in the early morning hours: sympathetic nervous system activity ramps up, renin and aldosterone levels rise before you even open your eyes, and your blood vessels’ ability to relax is at its weakest. Even healthy people show reduced blood vessel flexibility in the morning. This natural surge is one reason heart attacks and strokes are more common in the first few hours after waking.
Caffeine, Alcohol, and Common Substances
A single cup of coffee can raise your blood pressure by up to 10 mmHg. The increase typically begins within 30 minutes of drinking it and peaks around one hour later. Regular coffee drinkers may develop some tolerance to this effect, but it doesn’t disappear entirely for everyone.
Alcohol raises blood pressure through multiple pathways, including increasing sympathetic nervous system activity and affecting hormone regulation. Heavy or frequent drinking is strongly linked to sustained hypertension.
Several over-the-counter medications also push blood pressure up. Common pain relievers like ibuprofen (Advil) and naproxen (Aleve) cause the body to retain water and can strain the kidneys, both of which raise pressure. Decongestants found in cold and allergy products, including pseudoephedrine and phenylephrine, work by narrowing blood vessels to reduce nasal swelling. That same narrowing raises blood pressure throughout the body. If you take these regularly, they could be a hidden contributor.
How Exercise Temporarily Raises Pressure
During physical activity, your systolic pressure (the top number) naturally climbs as your heart pumps more blood to working muscles. Your diastolic pressure (the bottom number) should stay roughly the same or drop slightly. It’s normal for systolic readings to reach well above 160 or 170 mmHg during vigorous exercise. Values above roughly 210 mmHg in men or 190 mmHg in women during peak exertion have traditionally been considered an exaggerated response, though newer research suggests these thresholds should be adjusted by age, since younger adults typically peak lower.
This exercise-related rise is temporary and not harmful for most people. In fact, regular physical activity lowers resting blood pressure over time. The concern arises when post-exercise readings don’t return to baseline or when the spike during activity is far above expected ranges for your age.
Aging and Artery Stiffness
As you get older, your arteries gradually lose their elasticity. Healthy arteries stretch with each heartbeat and spring back, cushioning the force of blood flow. Over decades, the elastic fibers in artery walls break down and get replaced by stiffer collagen. Chronic exposure to high blood sugar accelerates this process by creating chemical cross-links between collagen fibers, making the walls even more rigid.
Stiff arteries can’t absorb the pulse of blood leaving the heart, so systolic pressure rises while diastolic pressure may stay the same or even fall. This pattern, called isolated systolic hypertension, is the most common form of high blood pressure in people over 60. Inflammation, oxidative stress, and the breakdown of elastic fibers all contribute to this progressive stiffening.
Medical Conditions That Raise Blood Pressure
When high blood pressure is caused by an identifiable underlying condition, it’s called secondary hypertension. Kidney problems are the most common culprit. Diabetes can damage the kidneys’ filtering system over time, leading to fluid and sodium retention. Polycystic kidney disease, where cysts interfere with normal kidney function, also raises pressure. Narrowing of the arteries that supply the kidneys, often from the same fatty plaque buildup that clogs coronary arteries, forces the body to compensate by driving pressure higher.
Sleep apnea is another major and often overlooked cause. Repeated pauses in breathing during sleep starve the body of oxygen, damaging blood vessel linings and triggering an overactive sympathetic nervous system. People with untreated sleep apnea often have blood pressure that’s resistant to standard treatments.
Hormonal conditions play a role too. When the adrenal glands produce too much aldosterone, the kidneys retain excess salt and water. Cushing syndrome, where the body makes too much cortisol (either from a tumor or long-term steroid medication use), also drives blood pressure up. Thyroid disorders, pregnancy, and even a rare birth defect that narrows the aorta can all be underlying causes.
Where the Thresholds Stand Now
The 2025 AHA/ACC guidelines define four categories:
- Normal: below 120/80 mmHg
- Elevated: 120 to 129 systolic with diastolic still under 80
- Stage 1 hypertension: 130 to 139 systolic or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic, or 90 or higher diastolic
If your top and bottom numbers fall into different categories, the higher category applies. These thresholds matter because they determine when lifestyle changes alone are recommended versus when additional intervention becomes appropriate. A single high reading doesn’t necessarily mean you have hypertension, but consistently elevated numbers across multiple readings do.