Endorphins bind to mu-opioid receptors, and sensitization of these receptors to endorphins leads to a greater positive feeling from subsequent endorphin release.

“endorphins bind to another type of receptor called the MU opioid receptor and when dorphin is released and you feel uncomfortable this causes new opioid receptors to make more of them and it's sensitizes them to endorphin so that means the next time that you make endorphin whether that's from exercise or the sauna because it also make uh cause you to release endorphin or if it's you know from laughter or giving someone a hug what whatever it is that's causing you to release endorphin you are going to feel so much better because that endorphin is going to bind to those receptors that are really sensitive to that endorphin and so the effects are lasting and they last longer and you feel better”