The list of 'triggers' in broad and includes viral infections, use of certain anti-fungal medications, exposure to sunshine on previously sunburned parts of the body, 'heat' events (like a sauna, hot tub, or hot showers), sweating, and stress. Some vaccines have triggered Grover's, and there even a couple dozen reported cases of the mRNA Covid vaccines or boosters triggering Grover's in people who never had the disease before. Could the strong magnetic field and radio waves generated by an MRI 'trigger' Grover's? With this disease I wouldn't rule it out.

As for jogging - keep running. Your overall health can't be sacrificed because of an uncomfortable, but not life-threatening, skin condition. My advice would be to buy some Gold Bond Extra Strength Medicated Body Powder and really powder up your abdomen, chest, shoulders, neck, and back before running. Wear a mask and goggles to apply the Powder, because it contains talc which you don't want to get in your sinuses, lungs, or eyes. The product contains 5% zinc oxide which provides an antimicrobial coating on your skin and prevents chafing and irritation. It also contains menthol to act as an analgesic, cooling your skin and reducing itching. Most important of all, it absorbs any sweat that your body produces during running so that the sweat is not left in contact with your skin. There are lots of theories about what 'causes' the itchy red bumps and lesions, but some of the proteins in your sweat are often the culprit. So powder up, go for a run, then wash off the powder with a cool shower as soon as you are done. I follow that routine for my aerobic and weight lifting sessions without experiencing any flareups. Once the five days of 50mg prednisone had stopped the inflammation and given me back clear skin, I found that weight lifting without using the body powder resulted in an itchy, prickly, minor 'heat rash' that later turned into red bumps. After a second round of prednisone to clear up the inflammation I won't make that mistake again. I keep up the routine of daily (disgusting) cilantro smoothies and I've been fine for some time. Good luck with your situation. Some doctors don't want to prescribe a drug that turns off your immune system because of the Covid pandemic, but if you do a high dose for five days your immune system bounces back within a few weeks. I've attached a picture of my chest/shoulder the day I started Prednisone, and then on day five of taking Prednisone.