When your face touches or is submerged in cold water, receptors in the nose and sinuses send a message to the brain through the trigeminal nerve.

This message tells the brain that you are underwater, and the brain tells the body to conserve oxygen.

The body conserves oxygen by:
* Slowing breath rate
* Slowing the heart rate (bradycardia)
* Constricting blood vessels in the limbs and other non-essential organs
* Dilating blood vessels in the heart and brain

These changes help to adapt and survive longer in cold temperatures.

When you get out of an ice bath, your body goes through a number of changes in an attempt to warm up. It is important to slowly and naturally let your body heat up:​​​​​​​​​

• To avoid a drop in blood pressure: When you get out of an ice bath, your body temperature will rise quickly. This can cause a drop in blood pressure, which can lead to dizziness, lightheadedness, and fainting. Warming up slowly helps to prevent this drop in blood pressure.

• To avoid muscle cramps: When your muscles are cold, they are more likely to cramp. Warming up slowly helps to warm up your muscles and reduce the risk of cramps.

• To improve circulation: When you get out of an ice bath, your blood vessels will constrict. This can reduce circulation and make it harder for your body to recover. Warming up slowly helps to dilate your blood vessels and improve circulation.

• To feel better: After an ice bath, you may feel cold, stiff, and tired. Warming up slowly helps to improve your mood and energy levels.