Hi,
Noted your history of developing red circle with inner white on scratching the leg, grown overnight, pale inner circle, not sore to touch, no tetanus shot in 20 years.
Your history is suggestive of an insect bite that caused the itching and scratching, the intense reaction on inner part is due to edema of the subcuticular tissues he periphery shows
redness as a part of reaction but with less edema allowing the redness to show up.
The Tic-sting can cause such encircled in two colors and thus I would advise you the following:
Consult your Doctor immediately so that a clinical inspection can tell whether this is due to tic or anything else, investigations in such a way to know the cause and get treated in general by an antihistamine and oral
steroid and antibiotic if tic is diagnosed to cause this problem.
Take
Tetanus toxoid too.
Do not apply anything locally as this changes the character for the Doctor to diagnosed well.
Complete the courses of antibiotics and other medications as would be advised fully to get n appropriate cure and avoid complications.
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. T. Chandrakant, General Surgeon