sentences:  They work by decreasing the production of androgen hormones by the ovaries and by decreasing the free and hence biologically active fractions of androgens, resulting in lowered skin production of sebum and consequently reduce acne severity.First-generation progestins such as norethindrone and norgestrel have androgenic properties and can worsen acne.Although oral estrogens decrease IGF-1 levels in some situations, which could theoretically improve acne symptoms, combined birth control pills do not appear to affect IGF-1 levels in fertile women.