The conversion of androgens such as testosterone into estrogens by the enzyme aromatase, mainly in fat tissue. Higher androgen levels mean more estrogen produced this way.
Some anabolic steroids aromatise readily, some weakly, and some not at all depending on their structure. Excess estrogen from aromatisation causes water retention, mood effects and gynecomastia in men. Too little estrogen, from over-suppression, harms bone, lipids, joints and libido. Estradiol on a blood test is how the balance is measured.
This article is for information and education only. It is not medical advice and does not replace a consultation with a physician. Anabolic-androgenic steroids are prescription medicines in most countries and are controlled substances in many. Check the law where you live.