Women who are being treated for breast cancer are often prohibited from using traditional hormone replacement therapy because breast cancer can be sensitive to estrogen, the predominant female hormone.
Because the most common types of breast cancer depend on estrogen to grow, experts once feared that soy isoflavones could stimulate the estrogen receptors in breast-cancer cells, even though the estrogens in soy are much weaker than those produced by the body.
Julie Russak, a dermatologist in Manhattan and clinical instructor at Mount Sinai School of Medicine, said it's understandable why the FDA would be cautious in approvals for new sunscreen ingredients because of a paucity of research and concerns that some may be highly allergenic or affect estrogen levels.