Oily skin gets treated like a personality trait — you're just an oily-skinned person. It's not. It's a signal, and in adult women it almost always points to one of two biological drivers.
Elevated androgens. Testosterone and DHEA-S drive sebum production directly. If you have oily skin plus jawline acne plus subtle androgen signals (chin hair, cycle irregularity, scalp thinning), androgens are probably in the story. PCOS is the most common underlying pattern.
Elevated insulin. Insulin drives IGF-1 signaling, which ramps up sebum. This is often the more common pattern in women in their thirties and forties who never had oily skin before. Fasting insulin can shift years before HbA1c or glucose do, and elevated insulin often produces oily skin, skin tags, larger visible pores, and adult acne together.
Chronic cortisol. Amplifies both androgen and insulin signaling. Chronic stress patterns don't produce oily skin directly, but they make everything downstream worse.
The measurable version of this workup: fasting insulin, HbA1c, and (through your physician) total and free testosterone plus DHEA-S. The combination tells you which pattern is driving it.
Fasting insulin is on the JenSkin panel — usually the highest-value starting point for an oily-skin workup.