Thanks for opting healthcaremagic.com to post your queries and giving us this opportunity to answer your questions.
Well, from what you tell us, that lesion on your sons axilla
has many differential diagnosis. But to confirm the diagnosis, we need to know some other history like :
1) Are there any other similar lesions ANYWHERE else on the body?
2) Does anyone else in the family have a history of similar skin lesions?
3) Does the skin lesion itch or pain or any reddness or increases or decreases in size ?
4) Is it increasing inspite of the treatment by the dermatologist?
Well, answers to all these questions and a visual impression along with a skin scrapping examination under a microscope will definitely help us to confirm your diagnosis. Since it is progressively increasing in size, i would recommend you to re-visit your peadiatric dermatologist and get your diagnosis confirmed before continuing the same treatment without any improvement.
I hope I have been successful in clarifying your doubts and I also will be available for any further queries if at all... Take care and stay healthy.