An article on the Mayo Clinic's website stated that dermographia can be triggered in some people by infections, emotional upset or medications such as penicillin. (Could other antibiotics be a trigger as well?)
Also have you been tested for food or environmental allergies? Allergies to gluten, white flour, wheat, eggs, peanut butter etc. are all common allergens that trigger skin problems.
Some of the underlying causes of a skin problem I have had, were medications, some supplements, but definitely the biggest contributor to my outbreaks (very red, patchy skin) was my diet.
Coffee, tea, soda or any kind of diet soda, sugar, sugary foods, and chocolate were all contributors to some extent. Adding fresh vegetables, some fresh fruits, coconut oil (both topically and internally) plus a fish/primrose/and borage oil capsule to my daily routine has helped clear up the problem.
However, of all the things I have used topically, coconut oil has been the absolute best product.
It is inexpensive, (usually found in the vitamin section of stores like Wal-Mart, but can be purchased online.) I use Spring Valley Organic Extra Virgin Coconut Oil - $10 - $12 dollars for 12 oz. I apply it topically in the morning, evening and more often if necessary.
Coconut oil is a solid by the way, unless the temperature gets into the 70s, then it will melt back into an oil. It is antibacterial and antifungal and has not yet caused me to break out. I take about a tsp. internally per day but it's best to check with a doctor before you make any major changes in your diet.
Regarding the cell phone -There are a lot of studies out there about cell phone radiation being linked or not linked to cancer or other problems. I've seen support for both sides of the coin, but why take a chance?
Hope that helps!