Sex hormone–binding globulin (SHBG) is a protein made mainly in the liver. It binds strongly to key sex hormones like testosterone, dihydrotestosterone (DHT), and estradiol. By doing so, SHBG controls how much of these hormones stay “free” (unbound) and biologically active in the body. Think of SHBG as a gatekeeper: it influences how much hormone is available to tissues in both men and women.
