I haven't felt the stinging from MSM, but I have felt it from other products I've taken. I also frequently feel an increase of stinging and itching after taking a dose of anti-parasitical herbs. My accupuncturist told me that is a good sign. It means the medicine is working when it pisses them off. He told me to increase it if I could tolerate more. I wouldn't stop taking the MSM if I were you. I've noticed that the first bite is the worst bite. After that, the stinging biting sensation is much milder and begins to subside in time. Sometimes it will come back if I increase the dose, or if I take a break from the medicine for a while and then start taking it again.