Cold water shock: the risk after a sauna and how to stay safe

What happens in cold water shock?

When cold water hits your skin, especially your chest and back, your body reacts in seconds:

• A big involuntary gasp, followed by
• fast, uncontrolled breathing that you can’t hold back, and
• a sharp rise in heart rate and blood pressure as blood vessels in your skin clamp shut.

The gasp is the biggest danger: if your head is underwater or a wave hits you, you can inhale water. Fast breathing can also make you panic and feel you can’t get enough air. The response peaks in the first 30 seconds and settles within a minute or two.

Why is it more of a risk after a sauna?

Many UK sauna clubs encourage a dip in the sea, a lake or a river between rounds. Coming from a hot sauna, your skin vessels are wide open and your heart is already working hard. The sudden switch to cold puts a short but large extra load on your heart. For healthy people this is usually fine, and many find it exhilarating. For people with heart disease, it can be dangerous.

Open water adds other risks: currents, waves, cold that saps your strength faster than you expect, and slippery steps.

Who should avoid cold plunges?

• People with heart disease, a history of heart rhythm problems or uncontrolled high blood pressure.
• People with Raynaud’s, whose fingers and toes can react badly to cold.
• Anyone who has been drinking alcohol.
• Pregnant women, unless their midwife or doctor is happy with it.
• Anyone feeling unwell.

If you’re unsure, ask your GP.

How to dip safely

1. Never go alone. Go with others, ideally at a venue with lifeguards or staff.
2. Enter slowly, using steps or walking in. Never jump or dive in after a sauna.
3. Breathe out slowly as the cold hits, and wait for your breathing to settle before going deeper.
4. Keep your head above water until the gasp has passed.
5. Stay close to the edge and where you can stand.
6. Keep it short: 30 seconds to 3 minutes is plenty for most people.
7. Warm up gradually afterwards with dry clothes, a hat and a warm drink, or back in the sauna.

If you get into trouble, remember the RNLI advice: lean back and float until your breathing calms, then call for help or swim to safety.

Is it hypothermia?

Not usually. Hypothermia, when core temperature falls below 35°C, takes much longer, typically 30 minutes or more in cold UK water. In short dips the risks are cold shock and, if you stay in for several minutes, losing strength and coordination in your hands and arms, which can make it hard to get out. Shivering, numb hands and slurred speech are signs to get out and warm up.