Medical term: Dermatographic urticaria. Also called "skin writing" for what should be obvious reasons. I started to really notice it in college. From my internet research, several things don't surprise me. It can start during times of stress (college wasn't a cake walk), it shows up in people who are fair skinned and don't tan (me), and also shows up in people who have other allergies (also me). At first, I just figured I had sensitive skin, and in some ways that's true. What's happening is the cells in my skin that hold histamines (which play a part in the immune system) have weak barrier walls and rupture without the presence of allergens. Even very light pressure or scratches can trigger a response like the one seen above. No worries though, the worst part about the condition is that it itches a little bit. It didn't hurt at all to write "hello" on my arm, I did it with the blunt end of a pen.
The other thing I did find out, because I got suspicious, is that people who have dermographism typically don't have scratch tests done to determine allergies. I had a scratch test done last year to try and figure out the cause of my EE (Eosinophilic Esophagitis), which is also allergy-related. At the time, I didn't know I had an official skin condition or I would have mentioned it to my allergist. I just knew my skin was sensitive and I did have to sit for 15-20 minutes after they scratched me (the average time it takes for my bumps to go down), so I didn't really think anything of it. They measured my "reactions" and the ones that I was "positive" for were based off measurements, not merely the presence of the bumps. The tree nuts and shellfish welts were HUGE, extremely obvious that I was allergic to those. The rest were all so-so. In the end, they decided I tested positive for those two plus corn, soy, and peanuts. I went on elimination diets of all those things to see if any of them were what was causing my EE. I was on several elimination diets for two weeks at a time (I think I might have spent 4-6 weeks eliminating total), and nothing actually helped. It wasn't until I got medication that the symptoms of the EE started to go away.
Remembering all this, a couple things come to my mind. Firstly, it is entirely possible that the corn/soy/peanuts results were false positives. Not that all allergies present in the same way, but whenever I've had an allergy to anything, I know it. I'm pretty in tune with my body. Corn does bother me, but mostly when it's by itself and not an ingredient in something (like corn chips). I grew up with soy sauce and peanut butter, neither of those things have ever bothered me in the slightest. Secondly, the elimination diets. The fact that nothing happened during those diets makes me lean even more towards the false positive idea.
When we have decent health insurance again (which will be this summer with any luck), I'll be going back to my allergist (or finding a new one) with this information and figuring out how to go from here.