I am managing a flat where the light bulbs in the one bathroom blow all the time. The tenants did not tell us and basically did not use the bathroom for three months as there is no window (no light). Now they moved out and we found out about it. I doubt the old tenant had bought a bulk pack of dodgy bulbs which might explain the problem, so there must be another reason.

What can be a possible reason why bulbs in one room/one fitting blow all the time?