The steroid hormones that are also called as gonadal hormones. The two main classes of sex hormones are androgens and estrogens. The most important human derivatives are testosterone and estradiol. Other contexts will include progestogens as a third class of sex steroids, different from androgens and estrogens. Progesterone is the important and only naturally-occurring sex hormone. Androgens are considered as "male sex hormones" with masculinizing effects, while estrogens and progestogens are considered as "female sex hormones" albeit at different levels.