I can understand your concern. Let me trll you that a presentarion similar to yours, especially as it is a skin related condition is always best to be physically examined and not diagnosed or treated without being looked at.
But based on the description some of the most common possibilities could be: fungal/yeast infections
(especially during summer), diabetes
, eczema, malignant melanoma
As you see the causes vary greatly. Which is why I would advise a quick scheduled visit to your doctor.
Wishing you great health.