All I can tell you is, it depends on the car, and location.
Most canisters have a safe operating temperature listed on them. It has nothing to do with the effectiveness of the OC, but the effectiveness of the delivery. If the temp is to low, the OC and it’s carrier can gel, and clog the nozzle. Additionally, and the bigger issue, the propellant used to pressurize the can will reduce in pressure and diminish the delivery force. If you get it too hot, it won’t really affect the consistency of the OC, but it will increase the pressure of the propellant and potentially burst the can. Basically think spray paint can, just a little less friendly substance being delivered. Get it cold, little blotchy droplets falling out of the nozzle, get it hot and boom.
I'm going through with my sister the different places she should have some pepper spray readily reachable. We both decided some should be in the car, easily within reach, in the console or other spot. She doesn't want to have to dig in her purse if somebody tries to carjack her.
So I was just considering the consequences of keeping the bottle in the car year-round. This is in NWI, where we get extremes in summer and winter.
Basically think spray paint can, just a little less friendly substance being delivered. Get it cold, little blotchy droplets falling out of the nozzle, get it hot and boom.
Sorry, didn't mean to thread jack. He just mentioned paint cans going boom and my mind instantly jumped to bigcraig dancing around trying to get out of the spray of green paint, from the punctured can at his feet.