Interestingly, a common culprit i found back when I was a massage therapist was men wearing their wallets in their back pockets and then sitting on them. All but 1 of my clients were men, and 70% of them spent long hours seated while traveling with wallet in back pocket, which puts pressure on the piriformis and impinges the sciatic nerve. A few others had injuries from carwrecks, physicslly work-related incidents, or from sports. Other sciatic clients had herniated lumbar discs so had to be referred elsewhere because massage directly to the affected area could make it worse. The best I could do in those cases was to apply ice (heat is bad for inflammation) and massage the glutes, hamstrings, and back areas above the inflamed location.