First, generally this isn't referred to as melasma because it isn't caused by the interaction of female hormones and light exposure.  Other causes can include genetic (other people in your family may have it), irritation from things like antiperspirants or chafing, etc., certain bacteria, or occasionally, illnesses like diabetes or prediabetes. Please see your doctor before treating this problem yourself!

Please also don't use the Renova, hydroquinones, etc here because they may irritate you (the skin is more sensitive here) and could make the problem worse!!   There are gentle ways to lighten the skin in these areas, but first you need an accurate diagosis about what may be causing it.   Dr. I