Nickel is possibly most insidious in this group of metals that produce estrogenic responses, since it is as potent as estradiol, and nickel often does not show up in hair analyses, even when severely poisoned. Thus, use of nickel in the underwires and fasteners of bras is particularly problematic, especially when combined with antiperspirant use, since the nickel would otherwise sweat out to help cleanse the breast of this contact carcinogen. Antiperspirants probably confound these effects, since aluminum and nickel may co-precipitate in the bone when magnesium is deficient. High levels of mercury in hair analyses of intractable breast cancer patients have been noted, and high copper has been observed in the hair analyses of prostate cancer patients.