Thanks for writing to us.
The appearance of welts restricted only to the tail bone may be allergic in origin or due to cholinergic nerve root
There is no permanent cure of this. For symptomatic relief, you can take oral anti allergics and anticholinergics.
Consulting a dermatologist
will be helpful in getting a specific treatment.
I hope this information has been both informative and helpful for you.
Dr. Rakhi Tayal