It's Fungus or yeast infection....common around skin folds like thighs and genitals.. avoid sweating, sharing clothes,towels and soap.. specific medicine required depends on the severity.. for detailed prescription do direct online consultation by sending photos.

P Alba is not a fungal infection , it’s mild form of atopic dermatitis. Coming to what u have mentioned as brown spots cannot confirm the diagnosis without proper examination as many conditions fall under brown spots.. but most common fungal infection we encounter is tinea Versicolor, which is mostly due to humidity.. if there is recurrence it’s better to go for antifungal pulse therapy..

There could b a remnant of fungal spores on clothes and your linen which could b a reason why there is a recurrence.