Reflection on immersion in mammals: what is it and what is it for

It is summer and one of the greatest pleasures of this period is to immerse yourself in the calm of the sea or the swimming pool. Although humans are not marine animals, we obviously lack the power to dive when the colder months arrive.

This calm submerged in cold waters has an evolutionary reason and we share it with other animals, especially mammals. This phenomenon is the immersion reflex of mammals and is essential to the survival of many marine animals.

Below, we’ll learn what triggers this reflex, what organic changes it involves, and how diving training influences one’s appearance.

    Immersion reflex in mammals: definition

    Sea or pool water gives us peace. It was upon entering this cold water that we began to feel deeply calm. This feeling is ancestral and has a very important evolutionary origin and is shared with other species of mammals. This is called the mammalian immersion reflex and Simply immerse yourself in cold water or throw it in your face to start activating pleasurable sensations.

    Although this reflection is a very striking link with other species of mammals, it is mainly present in aquatic mammals, such as seals, otters or dolphins, in which its appearance is a key condition for its survival. In humans, this happens in a very weakened way, but it always involves a series of changes at the organic level that make us stay longer than expected immersed in water, whether it is fresh or salty.

    Although it is called a mammal, it also seems to manifest itself in marine animals such as penguins, which has led to the hypothesis that its true origin would be in a common ancestor between birds and mammals. This would be a mechanism that proves the theory that birds and mammals come from the same ancestor and must live in water.

    How does this manifest itself?

    The mammalian immersion reflex it occurs whenever it comes in contact with water at low temperature, usually below 21 ° C. The lower the temperature, the greater the effect.

    too much it is necessary that, in order for this mechanism to be activated, water hits the faceAs this is where the trigeminal nerve is located, consisting of the ophthalmic, maxilla and mandible. It is these three nerve branches that can only be localized on the face, which, when activated, trigger the reflex, which involves the following processes in this same order.

    1. Bradycardia

    Bradycardia is a decrease in heart rate. When we dive we have to reduce the oxygen consumption and for this reason the heart starts to reduce the beats per minute by 10 to 25%.

    This phenomenon is directly dependent on temperature, so the lower the beat, the fewer beats there are. There have been cases of people only making 15-5 beats per minute, which is very low considering that the normal is 60 or more.

    2. Peripheral vasoconstriction

    Peripheral vasoconstriction or redistribution of blood involves transporting it to major organs, Such as the brain and heart. Blood capillaries are selectively closed, while those of major vital organs are kept open.

    The first capillaries to contract are those of the toes and hands, then give way to the feet and hands in their extension. Finally, those in the arms and legs contract, cutting off blood flow and letting more blood flow to the heart and brain.

    This minimizes possible damage from low temperatures and increases survival in prolonged oxygen deprivation. The hormone adrenaline plays a major role in this process, And it would be behind this that when we wash our face with very cold water, we wake up faster.

      3. Introduction of blood plasma

      Blood plasma is introduced into the lungs and other parts of the rib cage, causing the alveoli to fill with this plasma, which is reabsorbed when released into a pressurized environment. This way, organs in this region cannot be crushed by strong water pressure.

      Blood plasma is also produced inside the lungs. When diving at shallow depths, more mechanically, part of the blood enters the alveoli of the lungs. This protects them from increasing resistance to pressure.

      This phase of the diving reflex has been observed in humans, as would be the case with the freediver Martin Stepanek, during apneas over 90 meters deep. This way people can survive longer without oxygen under cold water than on land..

      4. Contraction of the spleen

      The spleen is an organ located behind and to the left of the stomach, the main function of which is the reserve of white and red blood cells. This organ contracts when the mammal’s immersion reflex occurs, causing it to release some of its blood cells into the blood, increasing its ability to carry oxygen. Thanks to that, temporarily increases hematocrit by 6% and hemoglobin by 3%.

      We have seen that in trained people, as would be the case with Estima, a Japanese and Korean diver who is dedicated to collecting pearls, the increase in these cells is about 10%, percentages close to what happens to marine animals when sealed.


      The mammalian immersion reflex is a mechanism that we humans have, ancestral evidence that we have a common ancestor between birds and other mammals believed to live in aquatic environments. Thanks to this reflection, we can survive submerged for a longer or shorter time, Formable as would be the case with Japanese and Korean estimates or, also, of the bajau of the Philippines, populations dedicated to spearfishing.

      While humans cannot be considered marine animals, the truth is, we can train our ability to dive. One can be overwhelmed for 10 minutes and there are even cases of people going over 24 minutes or more. Not only can you stay underwater for a long time, but you can reach depths close to 300 meters.

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