I am at an outdoor range and I am allergic to trees, grasses, etc. However...that is usually immediately accompanied by unstoppable sneezing, itchy eyes, etc. I do not have any itchiness or other "allergic" reactions. The range is pretty sparse when it comes to plants where I am at.
I did some research and it turns out that carbon monoxide is a component of the gases released from shooting. There are special ventilation requirements to reduce CO exposure at indoor ranges. I have experience headaches and flu like symptoms after shooting which are side effects of carbon monoxide. It is possible it is a lead reaction as well. I am always wearing long sleeves when at the range to reduce my exposure to hot brass and any lead.
I haven't had any updates as I've been too busy to get back to the range. I will update if I have any more developments. I will try a combination of things such as being at the range without shooting. Being at the range with the CO monitor. Being at the range with Claritin in my system, etc. It will take a while to do all these tests since the nearest outdoor range is an hour away.