Hello,
From the symptoms the possibility of erythrasma needs to be ruled out. It is true that groins are effected but the typical appearance is well-demarcated, brown-red macular patches. The skin has a wrinkled appearance with fine scales.
It has to be differentiated from contact dermatitis,eczema, sweat dermatitis and fungal infections which may mimic it. Wood lamp examination and gram staining are the tests for its diagnosis. So nothing can be confirmed without examination.
The standard therapy of erythrasma is antibiotics and antifungals because it is caused by a bacteria C minutissimum.Erythromycin is the drug of choice.
Mild steroids are helpful in reducing the inflammation associated with it. But use it only after a dermatologist,s prescription.
I hope it helps. Take care and regards.