Does a warm bath before bed help you sleep?

What does the evidence show?

Researchers at the University of Texas screened more than 5,000 papers and found 17 studies of warm baths or showers before bed, 13 of which had data they could combine.

They found that bathing or showering in water of about 40 to 42.5°C:

• improved how well people rated their sleep,
• improved sleep efficiency, the share of time in bed spent asleep, and
• when taken 1 to 2 hours before bed, for as little as 10 minutes, helped people fall asleep significantly faster.

The studies were mostly small, and people obviously knew whether they’d had a bath. But the results were consistent and fit what is known about body temperature and sleep, so we grade this moderate.

Why does warming up help you sleep?

It seems backwards, but it’s about cooling down. In the evening your body clock lowers your core temperature, and that fall helps bring on sleep. To lose heat, your body widens the blood vessels in your skin, particularly your hands and feet.

A warm bath widens those vessels. When you get out, blood keeps flowing near the surface and heat escapes faster, so your core temperature drops more quickly, in step with the body clock’s signal. Studies have shown that warm hands and feet, a sign of this heat loss, predict falling asleep faster.

How should you do it?

• Temperature: warm rather than hot, around 40°C. Use a bath thermometer if you have one; most people’s “hot” bath is warmer than this.
• Timing: finish 1 to 2 hours before bed.
• Length: 10 minutes or more.
• Afterwards: let yourself cool down in a cool bedroom; don’t pile on heavy bedding straight away.

Take care if you have a heart condition, low blood pressure or problems with balance, as hot water can make you dizzy. The NHS lists a relaxing bath as one of the ways to wind down in the hour before bed.