Further thoughts:
   - i have seen benadryl-based antihystamines powerfully repurposed
   between internal and external uses with great success in emergencies.
   - I have seen people crippled by allergies to things that are
   absolutely everywhere, and driven homeless, injured, and insane by
   this.
   - I have always been able to manage my allergies with careful and
   gentle management of exposure and willpower, to make them go away.
   Including poison ivy.  I have not met many other people to say this.  I
   also observe our medical culture to discourage trying it.  I am not
   myself interested in protective chemicals -- I would rather have the
   freedom to pursue gentle exposure, when the situation is not dangerous.
   - I am not asking others to go outdoors, or expose themselves to
   unpleasant things.