I'm still learning the ins and outs of wetshaving. I am working my way through a small sample pack of razor blades. After my last shave I had some irritation on my face and neck. Nothing too bad. Some redness and the feeling of a mild sunburn or something. I also tried a new aftershave. How can I tell if it is irritation from a razor that is not right for me or some kind of allergy to an ingredient in the aftershave? I'de rather not solve this by process of elimination.