This next skin condition is not nearly as serious as the one on the previous page and is never life-threatening, but it's rare and unusual just the same.
If you think you've got sensitive skin, you might think again after hearing about this condition. People with dermatographia have extremely sensitive skin, where even the slightest scratch or rubbing can cause the skin to react with raised red lines. It affects perhaps up to 5 percent of the population [source: Mayo Clinic]. Slight scratches will cause skin to swell and perhaps develop hive-like welts. The skin will often begin to itch uncomfortably.
Just to illustrate how severe it can be, people with this condition can literally write on their skin by lightly scratching it with their fingernails. Within minutes, distinct raised lines will appear, showing their writing with remarkable clarity. For this reason, the condition is also known as "skin writing."
Other things that can cause skin reactions are chafing from clothes as well as exposure to heat, cold or sunlight, or even experiencing emotion [source: Mayo Clinic]. Doctors aren't sure what causes dermatographia, but some speculate that it is some kind of allergic reaction.
Although the redness and welts will go away with time (30 minutes to a few hours), the symptoms can be painful, which is why doctors might recommend anti-histamines. The Mayo Clinic also suggests staying hydrated and using skin moisturizer, because dry skin only exacerbates the problem [source: Mayo Clinic].