Unexpected Lessons in Dermatotoxicology: De minimis Magnesium⁺⁺

By: Hongbo Zhai, MD, and Howard I. Maibach, MD, University of California

Posted: April 30, 2010, from the May 2010 issue of Cosmetics & Toiletries.

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The vagina is generally anaerobic. However, the production of TSST-1 is oxygen dependent; thus, no toxin is produced anaerobically. Tampons entrap sufficient air in the fiber mesh to introduce measurable amounts of oxygen into the vagina. Kass et al.⁵ demonstrated that at oxygen concentrations between 5% and 20%, excess amounts of toxin are produced if Mg⁺⁺ is limiting, and at higher concentrations of Mg⁺⁺, toxin production is uniformly decreased. In addition, higher incubation temperatures also increase toxin production; however, this effect is greatest at limiting concentrations of Mg⁺⁺ and is diminished when Mg⁺⁺ is present in excess.⁵

Fiber Absorption and Mg⁺⁺
Binding Polyacrylate fibers are highly absorptive but when treated with Mg⁺⁺ salts, the resulting fibers do not stimulate increased production of TSST-1, although their absorptive capacity is unchanged. In this manner, the Mg⁺⁺ combining capacity of a tampon can be separated from its absorptive capacity and thus, highly absorptive fibers can be treated to block the Mg⁺⁺ binding property. Typically, the peak time of onset of menstruation-related TSS is the fourth day. During early menstruation days, when flow is the heaviest, sufficient Mg⁺⁺ is present in the effluent to saturate the Mg⁺⁺ binding capacity of the fibers while leaving sufficient excess to keep toxin production at a minimum. Conversely, when menstrual flow is diminished, as occurs later in menstruation, the amount of Mg⁺⁺ entering the vagina is low and the fibers bind most of the Mg⁺⁺, leaving a low Mg⁺⁺ environment in which toxin production is promoted.⁵

Conclusions
In summary, Mg⁺⁺ has a powerful influence on bacterial multiplication and the production of TSST-1. TSS may associate with certain tampon brands but simple highly absorbent fibers are incapable of enhancing the production of TSST-1. When Mg⁺⁺ concentrations are limited, toxin production is increased, whereas with higher concentration of the Mg⁺⁺, the production of TSST-1 is suppressed.

Taken together, these insightful epidemiologic and mechanistic investigations of trace ions have explained an important and devastating problem that will assist developers of intimate care products. The lessons learned will also likely bear fruit for other issues of concern. The question now becomes: What will be next?

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