Heat and Cold Plunge – What Happens in the Body?

The short answer

Heat and cold affect the body in different ways.

In the sauna, the body works to get rid of excess heat. Blood flow towards the skin increases, perspiration is activated and the heart rate can rise.

When the body then meets cold water, the blood vessels close to the skin contract. Breathing can become faster, and both heart rate and blood pressure can change noticeably. This first reaction is usually called the cold shock response.

It is precisely the difference between these reactions that makes the change feel so pronounced.

Research shows that both heat and cold water can produce measurable physiological reactions. However, there is still not enough evidence to say that the combination generally provides particular long-term health benefits or is better than using the sauna alone.

Three stages of the experience

The change can be simplified into three stages:

The transition does not have to be quick. The first time in particular, it can be wise to pause, notice how you feel and only continue once your body feels stable. Read the guide to your first infrared sauna.

What happens during heat?

When the body is exposed to sauna heat, it works to keep its core temperature within a stable range.

The blood vessels in the skin widen and more blood is directed towards the surface of the body. The sweat glands are activated and the heart rate can rise as the body works to release heat. How strong the reaction becomes depends on factors such as the temperature, the length of the session, the type of sauna and individual heat tolerance. Read more about how an infrared sauna works.

In an infrared sauna, the air temperature is usually lower than in a traditional sauna and the heat often builds up more gradually. That does not mean the body stays cool. After a while, both the warmth and the perspiration can become noticeable. Read about the difference between an infrared sauna and a traditional sauna.

The experience of heat is individual. Some people begin to perspire quickly, while others need more time.

What happens in cold water?

Cold water cools the body considerably faster than cold air.

When a large part of the skin is suddenly cooled, the body can respond with an involuntary gasp, faster breathing, a higher heart rate and rising blood pressure. The reaction is particularly clear during the first moments and can become stronger the colder the water is and the more abrupt the immersion.

At the same time, the blood vessels close to the skin contract in order to reduce heat loss and keep warmth closer to the central parts of the body. This increases the resistance in the blood vessels and can temporarily mean more work for the heart.

That is why a cold plunge can feel very intense even when it only lasts a short while.

Why can the contrast feel invigorating?

When the body meets cold, a clear stress response is activated. Your attention turns to your breathing, your skin and the immediate situation.

Some people describe a sense of sharpness, energy or improved mood after a cold plunge. Research on cold water exposure has also examined possible changes in areas such as stress, well-being and quality of life.

The findings are interesting, but the evidence still consists of relatively few randomised studies, small groups of participants and varying methods. It is therefore not possible to promise that everyone will have the same experience, or that any effect will last.

For many people, the most noticeable thing is simply the contrast: from warm and heavy to cold and clear.

That is a subjective experience, not proof that the body has been cleansed or has undergone a medical treatment.

What does research say?

Research on saunas and research on cold water exposure are two partly separate fields.

Some studies have examined the immediate reaction when a sauna is followed by cold water. In one controlled study, heart rate and cardiac output rose after heat and a cold plunge, while systolic blood pressure fell during the sauna and then rose when the participants entered the cold water. The study included both healthy control participants and people with heart disease, and it shows that the change in temperature can produce clear circulatory changes. The findings cannot, however, be used as evidence of long-term health effects.

A more recent study of healthy women examined repeated rounds of Finnish sauna and cold water. There too, heart rate and blood pressure changed during the protocol. The study describes acute reactions within a specific arrangement, not a general prescription that suits everyone.

There is therefore evidence that the body reacts clearly to the change.

There is not, however, sufficient evidence to say that the combination:

• strengthens the immune system in any guaranteed way
• detoxifies the body
• provides lasting improvements in circulation
• burns fat to any meaningful degree
• treats inflammation or illness
• is better than the sauna alone
• suits everyone

The most responsible approach is to see heat and cold plunging as two different experiences that can be combined by those who enjoy the contrast and tolerate it well.

Do you need to cold plunge?

No.

A session in the infrared sauna is a complete experience even without a cold plunge. You do not need to finish in cold water for the sauna to have been worthwhile.

Some people appreciate the feeling of contrast. Others prefer a shower, a calm pause or simply letting the body cool down gradually.

Your choice may depend on:

• how you usually respond to cold
• how warm you have become
• how you feel that day
• how confident you feel in cold water
• your health and any medical risk factors
• whether you are looking for a clear contrast or a calm wind-down

Recovery does not have to be intense in order to feel valuable.

How to begin calmly

Your first time does not have to be about getting down to your shoulders or staying in for a certain length of time.

Let your body settle after the heat

Stand up calmly when you leave the sauna. Sit or stand for a moment and check that you do not feel dizzy or unusually weak.

Heat and perspiration can contribute to fluid loss. Thirst, a dry mouth, tiredness, reduced urine output and darker urine can be signs of dehydration.

Lower yourself in a controlled way

Lower your body at your own pace rather than jumping in.

The first contact with cold water can cause an involuntary gasp and faster breathing. Keep your face above the water and focus on making your breathing feel manageable before you go any deeper.

Holding your breath while lowering your face into very cold water can activate conflicting nerve reflexes and increase the risk of heart rhythm disturbances. There is no reason to submerge your head in order to have a complete experience.

Start with a short time

There is no exact length of time that suits everyone.

The temperature of the water, how warm you are, your build, your experience and your state of health all affect how quickly the cold becomes demanding. Start with a shorter time than you think you need and leave the water while you still feel in control.

A longer time is not automatically better.

Get out while you feel well

Do not wait for strong shivering, numbness or pain.

The purpose is not to test your willpower. A short and controlled dip can be more suitable than staying in until your body feels exhausted.

How cold does the water need to be?

A cold plunge does not have to mean the lowest possible temperature.

The colder the water, the faster the skin cools and the stronger the initial cold shock response can be. Research also uses different temperatures, durations and types of immersion, which makes it difficult to state a single optimal level.

For a beginner, it is better to focus on:

• controlled breathing
• a stable feeling in the body
• short exposure
• a safe way out of the water
• finishing before any discomfort becomes strong

The temperature is not a performance.

Should you finish warm or cold?

There is no ending that is right for everyone.

Finishing cold can give a clear and invigorating feeling. Finishing warm, or letting the body cool down gradually, can feel gentler and more relaxing.

Choose based on:

• how your body feels
• what you are going to do afterwards
• your experience
• whether you tend to feel cold for a long time after a cold plunge
• the feeling you want to take with you from your visit

After a cold plunge you should dry yourself, dress warmly and give your body time to return to a comfortable temperature. Do not try to speed up the rewarming with extreme heat if your skin feels strongly chilled or numb.

When should you stop?

After the sauna, you should skip the cold plunge if you already feel dizzy, dehydrated, unusually tired or unsteady.

Who should take extra care?

Cold water exposure can place a considerable load on the heart and circulation, because heart rate, blood pressure and vascular resistance can change quickly. People with cardiovascular disease may respond differently or be more sensitive to that load.

Consult your healthcare provider before combining a sauna with a cold plunge if, for example, you:

• have heart or vascular disease
• have high, low or unstable blood pressure
• have heart rhythm disturbances
• have experienced fainting
• have reduced sensation
• have a condition that affects temperature regulation
• are pregnant
• have kidney disease
• take medication that affects blood pressure, heart rate or fluid balance
• are unsure whether strong heat or cold is suitable for you

Do not use a cold plunge in combination with alcohol or other substances that impair judgement or physical control.

This article does not replace individual medical advice.

After heat and cold

Give your body time after the change in temperature.

Dry yourself properly, put on dry clothes and drink water. If you have perspired a great deal in the sauna, your body needs to replace the fluid it has lost.

It is normal for the skin to feel cold while the inside of the body still feels warm. Some people also continue to feel cool for a while afterwards.

Let recovery happen calmly. You do not need to add more rounds simply to follow a particular protocol. See what is good to know before your visit.

A single short change can be enough.

Frequently asked questions

Heat and cold plunge at Solportalen

At Solportalen you can let the warmth take centre stage, or choose to complement your sauna session with a cold plunge according to the current options for your booking. See sauna, cold plunge and current prices or read more about the cold plunge.

You do not need to follow a fixed protocol or complete several rounds. Begin calmly, listen to your body and choose the experience that feels right for you.

For some people, the cold plunge becomes a clear and invigorating finish. For others, the calm warmth and the wind-down are what matter most.

Both ways are equally valid.