Why is self-harm a feeling of relief?

Scientifically, self-harming gives a feeling like that due to the release of dopamine in the brain. Dopamine is a chemical in our bodies that causes a feeling of relief or relaxation or even just flat out happiness. However you have to be very careful because it can easily become like an addiction, where someone does it so often that the initial cut like normal isn't enough, so they have to cut deeper or more to get the same feeling. That's extremely dangerous.

No, it isn't. It may provide relief from the frustration for the time being, but in the long run, it will ruin you.

When you get hurt your body releases endorphin to your brain to calm you, this is a type of drug and you can become addicted to it just like any other drug.

The physical pain of self-harm takes away from someone’s mental pain temporarily, and this is relieving.

Self-harm might feel as a feeling of relief for people who can't or don't know how to get their sadness out so they think that grabbing a blade and slicing their skin is going to help them

generally people tend to inflict self harm upon themselves when they are feeling an array of emotions and troublesome thoughts. as by doing so momentarily, the individual is no longer focusing on these emotions and thoughts but rather the pain they felt when they hurt themselves. in other words it gives you a vent to let go of all these feelings and thoughts that were stirring in your mind. however, subconsciously these feelings and ideas are still there its just that for a moment you have pushed them into the back of your mind. as a result, inflicting self harm gives a sense of relief.