I'm a skin writer! It also known as Dermatographic urticaria if we want to use the scientific term or dermatographia for short. I am among one of the rare people who have this condition since it affects up to 5% of the population. When my skin gets lightly scratched on any part of my body, the scratches redden and become raise kind of like hives. The cause of Dermatographia is unknown unfortunately and can be triggered by infections, other allergies such as in my case, and medications. Symptoms and signs to look for are itching, swelling, hive-like welts can occur anywhere, raised red lines. I've had these pesky, painful scratches turned to welts show up on my arms, behind my knees, and recently on my right lower back/hip. This can last anywhere from a few minutes to several hours and days. Rubbing from clothes or bedsheets can irritate the skin as well. If you need to visit the doctor they will scratch your arm lightly and see if a red swollen line appears within a few seconds to minutes. If it does then the patient has Dermatographia. This happens to me every time I get scratched. The symptoms usually will go away on their own but if it is bothersome then the doctor will prescribe an antihistamine like Benadryl, Allegra, or Zyrtec. To prevent symptoms, refrain from using harsh soaps on the skin, don't wear wool, hot showers can worsen symptoms so take them luke warm, try to avoid scratching though it might be hard it only makes it worse, and keep the skin moisturized with lotion or creams.