Why do rubber bands turn cold and purple when they are tied around fingers?

We often see news reports about 3-4 year old children who accidentally tied their fingers with rubber bands while playing with them, and then forgot to take them off after falling asleep, which nearly led to amputation. If you are observant, you must have also discovered that when you tie your fingers with rubber bands, your fingers will become cold and purple after a few seconds, and after you remove the rubber bands, your fingers will become hot and red again.

How can a small rubber band be so powerful? Let's talk about it today.

01

Why do rubber bands turn cold and purple when they are tied around fingers?

Why do rubber bands turn your fingers cold and purple? Simply put, it's because of oxygen supply . Why is oxygen supply so critical?

Let's briefly review how the human body supplies energy. We know that all the energy in the human body comes from cellular respiration, which produces a "universal currency" - ATP.

There are two ways to produce ATP:

(1) C6H12O6 (glucose) + 6O2 → 6CO2 + 6 H2O + 38 ATP

(2) C6H12O6 (glucose) → 2C3H6O3 (lactic acid) + 2 ATP

Take a closer look at the difference between 1 and 2.

First, the reaction equation on the left has differences with and without oxygen.

1. The first one has oxygen, the second one has no oxygen.

2. The first is aerobic respiration, and the second is anaerobic respiration

Unless you are in pure oxygen conditions and your body is completely impossibly free of obstacles, the human body has always been both. If you don't believe it, go read a book. At most, when you are doing high-frequency and high-load exercise , resulting in insufficient oxygen intake, your anaerobic respiration will increase, that's all.

Therefore, if you want to enhance anaerobic respiration, just increase the frequency of exercise , such as skipping rope.

Second, the product on the right is different.

1. The first one produced 38 ATP; the second one only produced 2 ATP, so the energy of anaerobic respiration was extremely low.

2. The second one produces lactic acid, so people will feel sore due to anaerobic respiration.

Well, at this point, the principle is actually very clear.

02

Why does it feel cold when you tighten it, but warm when you loosen it?

Because after tightening, blood circulation cannot be supplied, and the most important function of blood is to carry oxygen.

Without oxygen, cellular respiration becomes anaerobic respiration, and the energy is only one-nineteenth of the previous one, so it is bound to get colder. Once you relax, oxygen comes up and the heating is immediately increased.

Sing with me:

You are in the bright sunshine in the south, and it is snowing heavily. I am in the cold night in the north, and it is spring all year round.

03

Why does it turn purple when tightened and red when loosened?

To answer this question, you can think about the color of blood. Because of the different oxygen contents, arterial blood is rich in oxygen and bright red in color, while venous blood is less oxygenated and dark red in color.

Therefore, when you tighten the muscles, the blood in the local capillaries cannot get in touch with fresh oxygen, so it gets darker and darker. When you release the muscles, oxygen rushes to your face, so the blood quickly comes in contact with oxygen, and the color is restored.

Imagine a medical illustration, with blue representing veins and red representing arteries.

Finally, a piece of advice is not to try it, because you can't control the time well, and if it lasts too long, it will cause local ischemia and necrosis.

Once this happens, you have no choice but to cut it off.