Heat raises blood pressure in most people, sometimes significantly

Yes, heat can raise your blood pressure. When you are exposed to high temperatures, your body works harder to cool itself down. Blood vessels near your skin widen to release heat, and your heart pumps faster to move blood to the skin's surface. This increased heart rate and the stress on your cardiovascular system can push your blood pressure up by 5 to 10 points or more, depending on how hot it is and how long you stay in the heat.

The effect is temporary in most cases — your blood pressure usually returns to normal once you cool down. But if you already have high blood pressure or take blood pressure medication, heat can be a real concern. Heat can also make your existing blood pressure medication less effective, which is why summer months sometimes bring higher readings at doctor visits.

People with hypertension are at higher risk during heat waves because the combination of heat stress and an already-strained cardiovascular system can lead to dangerous spikes. This is especially true for older adults, who have a harder time regulating body temperature and are more likely to be on multiple medications.

Key Takeaways

  • Heat causes blood vessels to widen and your heart to work harder, which can raise blood pressure by several points in most people.
  • The blood pressure rise from heat is usually temporary, but people with hypertension should monitor readings more closely during hot weather.
  • Some blood pressure medications become less effective in heat, so your doctor may need to adjust your dosage or timing during summer.
  • Staying hydrated, limiting time in direct heat, and keeping cool indoors during the hottest parts of the day are the main ways to protect yourself.
  • Heat waves pose a real health risk for older adults with high blood pressure, and you should know the warning signs of heat-related illness.

Why heat affects blood pressure differently in people with hypertension

Your body's response to heat is automatic — it is designed to keep your core temperature stable. When the outside temperature rises, your blood vessels dilate (widen) to allow more blood to flow to your skin, where heat can escape. Your heart has to pump harder to move this extra blood volume, and your nervous system releases stress hormones that constrict some blood vessels while others open. For someone without hypertension, this system usually works well enough that the temporary rise is minor.

If you already have high blood pressure, your blood vessels are stiffer and less flexible than they should be. They cannot dilate as smoothly, so your heart has to work even harder to push blood through them. The heat adds another layer of stress on top of an already-strained system. Your body is also working to cool itself while your cardiovascular system is already under load, which can create a compounding effect.

Dehydration makes this worse. When you lose fluids through sweating, your blood becomes more concentrated, which naturally raises blood pressure. If you are not drinking enough water in the heat, you are making your hypertension harder to control.

How blood pressure medications interact with heat

Several common blood pressure medications are affected by heat. Diuretics — water pills like hydrochlorothiazide (HCTZ) or furosemide — work by reducing the amount of fluid in your bloodstream. In hot weather, you are already losing fluids through sweat, so a diuretic can push you toward dehydration faster. This can actually raise your blood pressure instead of lowering it, or cause dizziness and weakness.

Beta-blockers like metoprolol or atenolol slow your heart rate and reduce the force of your heartbeat. They can interfere with your body's ability to cool itself because they prevent your heart rate from rising as much as it needs to during heat exposure. This means your body has a harder time regulating temperature, and you may overheat more easily.

ACE inhibitors and ARBs (like lisinopril or losartan) are generally safer in heat, but they can still contribute to dehydration if you are not careful about fluid intake. If you take any blood pressure medication and notice that your readings are higher during summer, or that you feel dizzy or weak in the heat, tell your doctor. They may adjust your dose, change the time of day you take it, or switch you to a different medication during hot months.

What to do if you have high blood pressure during a heat wave

The first step is to stay out of the heat as much as possible. If you have air conditioning, use it. If you do not, spend time in public places that are air-conditioned — libraries, shopping centers, community centers, or cooling centers that many cities open during heat waves. Even a few hours in a cool environment can give your body a break and lower your blood pressure.

Drink water regularly throughout the day, even if you do not feel thirsty. Aim for at least 8 to 10 glasses a day, more if you are sweating. Avoid alcohol and caffeine because both can dehydrate you and raise blood pressure. If you are on a diuretic, ask your doctor whether you should drink more water than usual during hot weather.

Wear light-colored, loose-fitting clothing and stay in the shade when you are outside. Take cool baths or showers to bring your body temperature down. Check your blood pressure more often during heat waves — once or twice a day if you have a home monitor — so you can catch any dangerous spikes early. If your readings are consistently higher than usual, contact your doctor before making any changes to your medication.

Warning signs that heat is affecting you dangerously

Heat exhaustion and heat stroke are medical emergencies, and they happen faster in people with high blood pressure. Know the difference: heat exhaustion causes heavy sweating, weakness, dizziness, nausea, and a normal or slightly elevated body temperature. Heat stroke is more serious — you may stop sweating, feel confused, have a very high body temperature (above 103°F), or lose consciousness.

If you feel dizzy, faint, have chest pain, shortness of breath, or a severe headache during hot weather, get to a cool place when ready and call 911 or your local emergency number. Do not wait to see if it passes. These can be signs that the heat is causing a dangerous spike in blood pressure or a heat-related emergency.

Older adults sometimes do not feel thirsty even when they are dehydrated, so set reminders to drink water throughout the day. If you live alone, ask a family member or friend to check on you during heat waves. Many communities have programs that call seniors during extreme heat to make sure they are staying cool and hydrated.

When to contact your doctor about heat and blood pressure

Contact your doctor if your blood pressure readings are consistently 10 to 15 points higher during hot weather than they are in cooler months. This is common and often manageable with small changes, but your doctor needs to know so they can adjust your treatment plan if needed.

You should also reach out if you feel unusually tired, dizzy, or weak during heat, especially if these symptoms are new or getting worse. These can be signs that your medication is not working well in the heat or that you are becoming dehydrated. Your doctor may recommend checking your blood pressure at different times of day to see when the spikes happen, or they may suggest keeping a log of your readings along with the temperature and what you were doing.

If you take a diuretic and notice that you are thirstier than usual or that your mouth feels dry, tell your doctor. Do not stop taking your medication or change your dose on your own — your doctor needs to make that decision based on your individual situation.

Frequently Asked Questions

Does air conditioning help lower blood pressure?

Yes. Staying in a cool environment reduces the stress on your cardiovascular system and allows your blood vessels to function more normally. If you spend several hours a day in air conditioning during a heat wave, your average blood pressure readings will likely be lower than if you were exposed to heat all day.

Can I exercise outside in hot weather if I have high blood pressure?

Exercise is important for managing hypertension, but hot weather adds extra stress to your heart. Exercise early in the morning or later in the evening when it is cooler, stay hydrated, and wear light clothing. If you feel dizzy, short of breath, or have chest pain, stop when ready and move to a cool place. Talk to your doctor about what is safe for you.

Will my blood pressure go back to normal once I cool down?

Usually, yes. For most people, blood pressure returns to baseline within an hour or two of cooling down. But if you have been in extreme heat for a long time or are severely dehydrated, it may take longer. If your readings stay high even after you have cooled down and rehydrated, contact your doctor.

Is it safe to take my blood pressure medication during a heat wave?

Yes, keep taking your medication as prescribed unless your doctor tells you otherwise. Do not stop or skip doses because of the heat. If you are concerned that the heat is affecting how your medication works, call your doctor to discuss it — they may adjust your dose or timing, but that decision has to come from them.

What should I keep in my home during hot weather if I have hypertension?

Keep plenty of water on hand, a working thermometer to check your body temperature, and your blood pressure monitor if you have one. Have a list of emergency numbers posted where you can see it, and make sure someone knows to check on you during heat waves. If you do not have air conditioning, know where the nearest cooling center is located.