Thanks for the query,
Smell in armpit and anal area mainly occurs due to corynebacteria overgrowth.
These bacteria breakdown the lipid and produce smell.
You need to apply an anti bacterial powder to remove this odor as well as reduce the sweating.
A culture for bacterial growth
will also be helpful.
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.