Skin Toxicology—The Future May Be Orange

By: Johann Wiechers, PhD, JW Solutions

Posted: July 9, 2010

It happened again—this time at the Skin Forum in Edinburgh, Scotland. This conference showcased different types of research involving skin but once again, as in many previous conferences, a toxicologist explained to the audience how to perform tests without adhering to scientific rules. Do the laws of science not apply?

The audience listened as an estimate was made for the concentration of a material penetrating the skin. This was calculated by multiplying the applied dose by the percentage of skin penetration, then dividing this result by the application area to calculate the local skin concentration. This compared to a level having no adverse effects, and from this, an estimate of the toxicological impact was made. Sounds okay, right? Think again!

People often forget is that it is wrong to express skin penetration in percentages. The toxicologist presenting gave an example of a metal (such as nickel), and asked the audience what the typical penetration would be: 100%, 10%, 1% or 0.1%. No one said anything. The presenter explained that normally his audience would respond 1%, and he subsequently showed that even skin penetration at only 0.1% was sufficient to kill the imaginary subject on the Powerpoint slide. He also used too large a number for the surface area of hands. Typically, the subjects used to make these calculations are thinner, thus leading to higher estimates than would be found in the body of more average subjects. This, too, sounds okay, right? Think again!

When the presentation was over, this author asked the presenter why toxicologists always express skin penetration in percentages and not in microgram per square centimeter per hour, as is done by skin delivery scientists. He answered, "Because we do."

The night before this conference, the Dutch national football team (soccer, for Americans) had defeated Uruguay in an exciting match in South Africa, winning the semi-finals. Had the match lasted 5 min longer, the Uruguayans may have won. Like many sports fans, the Dutch have a habit of painting their faces orange (and houses and cars, if their wives allow them) to contribute to a nationalist feeling especially since, for the first time since 1978, the Dutch are in the finals of the World Cup. (We lost the finals in 1974 against the Germans, and again in 1978 against the Argentineans). So, since the Dutch football team has made it to the finals again, 32 years later, some people would jump into a swimming pool of orange paint if they had one.