I have sjogren's syndrome. i am also allergic to insect bites. why does the "red area" seem to spread if i scratch it after a week of being bitten?

Red area: You may have dermatographia as part of your Sjorgen Syndrome. The friction of scratching will cause the "red area"to spread. The exact cause and mechanism is unknown

Dermatography: Wanda, usually the redness at the site of an insect bite is due to a local reaction. Scratching the area increases local histamine release, thereby making the redness spread. It should fade in time. Hope this helps!