What is really causing this rash?
RASHES in the natal cleft can be intertrigo, tinea or psoriasis. We usually think of psoriasis as being a red scaly disease, but when it involves the flexures with occluded surfaces the scale is lost, except at the outer edges. Tinea is rarely as symmetrical as this, while intertrigo with sweating can look very similar but there will not be any edge scales.
Sometimes psoriasis and intertrigo can be complicated by secondary candida infection. These will present as satellite pustules beyond the edge of the rash.