hmm... I couldn't find my last post on this topic. Sorry for the repost. I got a response and finally found it lol. Disregard this post- thanks
If it is a hole in the middle of back then it can be a sebaceous cyst but if it is at the lower end of back then it can be due to pilonidal cyst. A sebaceous cyst is a closed sac occurring just under the skin which contains a "pasty" or "cheesy" looking substance called keratin.They may occur anywhere on body but scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts.
Both require surgical excision by traditional wide excision, minimal excision, and punch biopsy excision. I suggest you to get it examined from a dermatologist.
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.