Androgens
A group of hormones, including testosterone, present in everyone. In PMOS they often run higher than typical, which drives several of the visible signs.
Androgens are a family of hormones that includes testosterone, DHEAS, and androstenedione. They are often called "male hormones," but everyone makes them, and they do necessary work in all bodies: bone, muscle, libido, and the normal function of the ovary.
In PMOS, androgens are frequently elevated, a state called hyperandrogenism. The extra androgens come mostly from the ovary, with a smaller share from the adrenal glands. Insulin amplifies ovarian androgen production, which is why the metabolic and androgenic parts of PMOS are so tightly linked.
Elevated androgens are behind several of the recognizable signs: acne along the jaw and chin, terminal hair growth in male-pattern areas, and scalp thinning. They also contribute to disrupted ovulation. Androgens can be measured in the blood, though what matters most is often the free, unbound fraction rather than the total.