Dermographia or Dermographism is a skin problem where you scratch and the place where you have scratched comes up in a red lump. I first noticed it in my daughter when she was getting ready to have a shower and used the back scratcher on her back. Every place she had scratched there was a line, a visible bump and a quarter of an inch each side of every line it was red. By the time she had scratched all of her back, it was a mess. I scratched my own arm and nothing happened, no redness, no bump. I realized she had a problem that I didn't have.
She seemed to scratch more in the mornings than the rest of the day. As the day went on she scratched less. But I was very annoyed by her constant scratching. The more I said, "Don't scratch" the less it helped. But the more she scratched, the more the red marks came up. They didn't last for long, maybe 10 or 15 minutes, but she frequently scratched her face so I often saw different combinations of markings on her face that didn't look good.
Before the day when I saw her back was a mess with the backscratcher scratching, I took her to see the doctor, I told the doctor that she was constantly scratching, but the doctor didn't seem to want to find a cause. In reality itchy skin is caused by so many different things, that it's hard for a doctor to quickly diagnose exactly the cause. She offered us an allergy test, but I declined. The doctor's theory was that she had grown into a habit of scratching and her skin wasn't really itchy at all. She suggested using the distraction technique.
So I searched the wonderful Internet. I searched for "red lines when scratching" and I quickly found the words dermographia and dermographism. When I read the descriptions they described exactly my daughter's problem. When you have dermographia and scratch lines appear, you can draw pictures on your skin. It is in the urticaria family and is sometimes called Dermatographic Urticaria. In my daughter's case the welt caused when scratched lasted 10-15 minutes, but in other people it can last longer, even days. It is an allergic reaction to something, but most people never discover what. It is not contagious and cannot be passed from one person to another. Changing soap or soap powder may help relieve symptoms.
In my daughter's case she noticed she was more itchy after using shampoo. She was at the time using a well known brand of kids' shampoo, when she used my regular shampoo she was less itchy. She stopped using the kids' shampoo and everything improved. She still has dermographia, but she doesn't scratch much any more.