Tirz Suddenly Starts Stinging

It might be that the person is pausing too much before injecting, which makes it worse. Just do a quick jab without overthinking. If the pain comes after, it could be a reaction at the site, but this seems more like hesitation. Alcohol from the wipe not being dry can also sting. Or maybe the needle is getting dull from multiple uses on the vial.

You should check the pH with test strips. If it's not close to neutral, that could be the issue. Is this some kind of homemade sterile water?

Stinging on needle entry often means the alcohol from cleaning hasn't evaporated yet so I give it time to air dry. A thicker needle could explain it too since finer ones usually cause little discomfort and maybe someone with medical training prefers those. Any burn while pushing in the substance feels like tissue reacting to the solution chemistry itself rather than the body responding right away. Certain compounds do that while others stay mild and the mixing liquid might have an off balance that adds irritation. Going in too close to the surface can hit more nerves as well. Body spots differ in sensitivity with the area beside the navel in the fat layer usually feeling okay. Simple test papers or even urine strips can show the acidity of the mixing liquid if I want to check. Discomfort that builds afterward might still come from chemical irritation or possibly an immune reaction which tends to bring some redness and swelling at the site.

Really great response, thanks a lot.

I've noticed that product from certain sources can cause stinging while others don't. Have you changed to a different vial lately? I'm quite sensitive myself, unlike the rest.