Fainting, Dizziness and Low Blood Pressure After Hot Water

Urgent Guidance First

In the US, call 911 if someone who has fainted is not breathing, cannot be woken within 1 minute, has not fully recovered, has chest pain or a pounding, fluttering or irregular heartbeat, has seriously hurt themselves, is having a seizure, or fainted while exercising or lying down. These are the NHS (UK) criteria for emergency help. [1] If someone faints in water, call for help at once; see drowning risk.

The NHS says fainting is not usually serious but anyone who has fainted should see a GP, to find out why. [1]

What Is Happening in the Body

The NHS lists causes of fainting including standing up too quickly (which it says could be a sign of low blood pressure), not eating or drinking enough, being too hot, being very upset or in severe pain, heart problems, and taking drugs or drinking too much alcohol. [1] Warning signs it lists include dizziness, sweating, feeling warm or hot, feeling sick and changes to vision. [1]

The NHS describes postural hypotension as low blood pressure that causes symptoms when you stand up or change position suddenly. [2] It lists some medicines among the causes of low blood pressure. [2]

Why Hot Water Can Add to This

A proposed explanation, from a 2026 review on bathing in older Japanese adults, is that in hot water the blood pressure of older adults first rises from water pressure, then drops during a long soak because heart rate does not increase as it does in younger people. It adds that on getting out, widening of blood vessels in the skin and limbs leads to further low blood pressure on standing, known as orthostatic hypotension. [3] That is the authors' explanation from a review of Japanese studies, not a clinical trial.

A 2026 narrative review of heat therapy (saunas, hot spring bathing, hot water immersion and mudpacks) found systolic blood pressure reductions of approximately 11 to 27 mmHg within 24 hours. It noted most included studies lacked control groups and varied in temperature, timing and populations. [4] It said a few small studies suggested larger drops in beta-blocker users. [4]

Medicines

A Finnish literature review of sauna bathing found medication generally was of no concern during a bath, apart from antihypertensive medication, which may predispose to orthostatic hypotension after bathing. [5] The review also said most of its data came from uncontrolled designs in people who had bathed since childhood. [5] Never stop or change your blood pressure medicine because of this; ask your prescriber or pharmacist about hot water and your medicines.

Cold Rooms Before Bathing

A real-world study of 1,479 older adults in Japan found that a lower living-room temperature before bathing was associated with higher skin temperature in the bath, which the authors say may produce excessive blood pressure and heart rate changes. [6] The authors report grants from several building-products and electrical companies, which is worth knowing when reading it. [6] This is cross-sectional data, so it shows an association only.

Falls

The 2026 review above links loss of consciousness in a bath to submersion and drowning. [3] The sources we read for this page do not give fall statistics for baths and hot tubs. Proper evidence not found for fall rates, after searching PubMed for bath-related deaths and orthostatic hypotension after hot baths. See getting in and out of water safely.

What the NHS Says to Do If You Feel Faint

If you feel like you are about to faint, the NHS advises lying down with your legs raised, or if you cannot, sitting with your head lowered between your knees, and drinking some water. [1] For low blood pressure symptoms, it advises getting up slowly from sitting to standing, and not changing posture suddenly. [2] It says that if someone has fainted and is breathing normally, lay them on their back and raise their legs; if they are pregnant, especially after 28 weeks, laying on their side is better. [1]