When a baby is vaccinated, he cries a few seconds after the injection. Is it a slow response?

For babies, all kinds of pain receptors have matured and are very sensitive to pain stimulation. Parents who have taken care of their babies may find that if the diaper is a little rough and the buttocks are a little red, The child will cry. It is easy to observe that babies have the ability to feel pain. Why do I wait until the injection is removed before crying during the injection? It's because it is true that it hurts when the needle is pulled out.

This conclusion is counter-intuitive. I only realized this after I got vaccinated last month. Because as an adult, when vaccinated, the pain becomes more severe after the needle is pulled out. In turn, it also confirms that the baby's reaction is natural.

So why does it start to hurt after the vaccine is taken out? What happened during the vaccination?

The vaccination we are talking about is actually an intramuscular injection of a drug. The doctor uses the needle of the syringe to pierce the skin, pass through the dermis, and finally reach the muscle tissue, and then push the vaccine (liquid drug) from the needle into the space between the muscle tissue. Then remove the needle. The whole process is very fast, and skilled staff can control the process within a few seconds.

The syringe used is a 1ml syringe with a 0.45mm diameter needle. This is a very thin needle model, even thinner than the usual scalp needles used for blood tests. The pain of acupuncture is related to the thickness of the needle. The thinner the needle, the less painful it will be. The feeling caused by the needle puncture for vaccination is similar to the moment of being bitten by a mosquito, and is lighter than the feeling of a venous blood test. This level of pain is tolerable to the child due to its short duration.

When acupuncture enters the skin, it physically stimulates skin receptors. These receptors convert the stimulation into signals, which are then transmitted to the brain through the nervous system, causing the sensation of pain. One characteristic of skin receptors is that in addition to a certain intensity of stimulation, a certain area is also required to awaken the receptors for conversion. This is why the finer the needle, the lighter the sensation. The duration of stimulation is also a factor that affects pain perception. Since the needle is pulled out within a few seconds, the sensation on the skin is not so intense that it is unbearable.

This is why children do not immediately show pain when the needle is inserted. Although they feel the needle when it is inserted, it does not reach the level of pain.

Then why does it start to hurt after removing the needle? It’s because the medicine reaches between the muscle fibers, and there are pain receptors in the muscle tissue. Different from the receptors in the skin, the receptors in the muscle tissue are slower, but more sensitive to chemical stimulation. When drugs enter the muscle tissue, they will strongly stimulate the chemical receptors, causing pain signals to continue to be transmitted to the brain to produce pain. In my personal experience, the pain is similar to when my arm hits a corner while walking briskly.

And the pain receptors inside the muscles have a characteristic of slow adaptability. What does this mean? That is, as long as the stimulation continues, the degree of pain will not decrease. In contrast to cutaneous receptors, cutaneous receptors are rapidly adaptive. If a stimulus is present without change for a long time, the receptors will reduce the intensity of the incoming signal. My personal feeling is that it lasted about 5 minutes before it started to ease. Because I received the same MMR vaccine as the children, the experience should be similar to that of the children.

So the stimulation of the drug in the muscle tissue is the reason why the child cries. This pain is more intense than the skin and lasts longer. It needs to be felt after the drug is pushed into the muscle. This is why Reasons why children cry later.

Of course, because older children have memories, they may recall the discomfort of the previous needle before getting the needle, so they may cry in fear. This is different from babies.

So if your baby starts crying after vaccination, don’t laugh at the baby, it really hurts. You can soothe your baby by giving him something delicious to eat or giving him a hug and a kiss. If you have a baby, sucking breast milk or a pacifier can make your baby feel better.