Have a circular rash on my butt

i dont know what this is, but  I've had this rash on my butt a week ago. I thought it was just an ordinary butt rash, but as days go by, it went big, circular, and crater feel when i touch it. the surrounding side is elevated and center is somewaht smooth. I got scared maybe its hiv or something coz i had unprotected sex 7 weeks ago. could you please help me identify this? i've searched online and thought its jock itch, or ring worm, or a chancre by syphillis (syphilis). its freakin me out. and at the same time, got a swollen lymph node on my left neck. not painful, sometimes it shrinks and gets enlarged again.

*its not itchy, and somewhat sensitive to touch.

[Bhupinder Kaur, MD]

Hello,

This rash on buttocks can be due to ringworm or nummular dermatitis. From the description (dry, red, itchy), it seems like nummular dermatitis but exact confirmation has to be done first. Steroids prescribed in nummular dermatitis can worsen the symptoms if it is ringworm. This can be confirmed by KOH examination of the skin scrapings and a skin biopsy done. If it is a fungal infection, then you may need topical and oral antifungals.

It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.