Dermatographia

Dermatographia is a condition in which you develop red, swollen ridges on the skin when it is stroked with a blunt instrument such as a fingernail. The condition results from damage to the body's immune cells, which release chemicals that cause the reaction.

Although dermatographia is associated with other types of allergic responses, it can exist alone. In your case, I suspect that both the hives and dermatographia are caused by the same thing.