A lot of people here might remember that, having kept bees for a number of years and receiving my fair share of stings without any adverse reaction other than the usual itchy red patch, I was stung once on the finger 18 months ago and less than 2 minutes later I'd collapsed, unconscious with worse to come. Usually I'd have been on my own, but by sheer luck my son was around to call an ambulance. 2 days in hospital later I was home but no memory of it.
I was very lucky to have a sympathetic doctor who referred me for immunotherapy treatment. I'm now in the maintenance phase of injections which will continue for another 2 years. I still need to carry epipens and have a very supportive husband who shares our beekeeping workload. I wear my full suit and gloves at all times, even with gentle colonies and swarms!
I was stung for the first time in the field a couple of weeks ago, through a stitched seam in my older gloves. I had my epipens out and ready, but I'm now over a year in with my immunotherapy and the sting was like they used to be, itchy, red, OK...
The point I wanted to make is, don't assume you're body is building up its own immunity just because you get stung as a beekeeper. Immune systems are fickle things.