Thanks for posting your query.
It could be due to sweating and humidity which gets access for Fungi to grow.
You see to that the area is always dry.
After taking bathe you wipe with dry towel and you can apply talcum powder in normal situations.
You can use topical fungal creams.
It can be prescribed only after being examined.
I suggest you to consult a Dermatologist
since local examination associated with investigations like microscopic examination of lesion scrapings are needed.
Hope I have answered your query.
Wishing you good health.