Yup, it is more of an individual thing. Its the same as how some dogs react to vaccinations while other don't.
Benedryl is something that you should always have in your doggy first aid. It needs to be plain Benedryl though.
Winston swells up if he gets an insect bite, while Digby doesn't. But then Digby gets nice sized welts from tick bites, while Winston doesn't.
The benedryl also came in handy last week when I discovered my dogs had gotten lice. Digby scratched to the point that he was giving himself hotspots
If your dog is having an allergic reaction giving Benedryl is the first step. Then its observation. If the dog is having issues breathing then its time to haul bootie to the vet where they can give an injectable antihistamine and assist with the breathing if neccessary.