Postherpetic neuralgia is a painful condition that follows an outbreak of shingles. The medical term for shingles is herpes zoster. That’s because the condition is usually caused by a herpes virus. Postherpetic refers to “after herpes.” Neuralgia is pain that extends along the course of a nerve.

The particular virus that causes shingles is the varicella-zoster virus. The virus caused chicken pox when you were younger. Varicella-zoster infects nerves, including the nerve endings in the skin. After hiding out quietly for many years in nerves, it can “reawaken” and cause shingles.

The revived infection causes inflammation. The result is pain and a rash that usually looks like multiple small blisters surrounded by redness.

All of the body’s nerves come in pairs, with one going to the right side and another to the left. Shingles usually happens in just one nerve. So it typically shows up on just one side of the body. Sometimes, though, multiple nerves are affected at about the same time. This is a condition called disseminated zoster. This usually happens in people with a weakened immune system. There can also be pain without the usual rash, and less often, a rash without the pain.

I am not sure if there is a connection between the rash on your arm and the pain in your face. If the rash on your arm looked like shingles and was accompanied by unpleasant sensations or pain, it was probably shingles.

But in your case, it’s possible that the rash under your arm was not shingles. And even if was shingles, the facial pain could be caused by something else. And it may not be from reactivation of the herpes zoster virus.

So the bottom line is that the arm rash and the face pain could have been connected or just a coincidence.