Sunday, November 9, 2014

Lost Keys Under Street Lamp Part II – Dermal Exposure

Chris Packham is a colleague from the UK who I met many years ago over there.  For as long as I have known him, and I am sure before that,  he has worked tirelessly trying to raise awareness of dermal exposure as an important source of risk to workers.  He is presenting a talk on the subject at a regional British Occupational Health Society (BOHS) meeting on November 18th and he has graciously allowed me to publish that talk in this blog afterwards.   

Before then he sent me an email which I am reproducing below on the general subject in which, I believe, he makes some very good points.

I continue to be frustrated at the apparent insistence by hygienists on concentrating on inhalation exposure and ignoring skin exposure, particularly when statistics show otherwise.
“Both the number of cases and the rate of skin diseases in the U.S. exceed recordable respiratory illnesses.

In 2006, 41,400 recordable skin diseases were reported by the Bureau of Labor Statistics at a rate of 4.5 injuries per 10,000 employees, compared to 17,700 respiratory illnesses with a rate of 1.9 illnesses per 10,000 employees.” - OSHA Technical Manual, Section II, Chapter 2
“Occupational skin diseases are among the three most frequent groups of occupational diseases. ... However, occupational skin diseases have attracted relatively little attention in the global and national agendas for prevention of occupational and work-related diseases. – World Health Organisation Global Workshop, Geneva, February, 2011
At a skin conference in Amsterdam in 2013 German statistics were presented showing that occupational skin disease represented 35% of all recognised cases of occupational ill health!

And that is just skin disease, ignoring the contribution that skin uptake  makes to systemic toxic effects.

Is it because hygienists believe that they can measure inhalation exposure and confirm compliance with the exposure limits?  As this is not possible with skin they do not feel comfortable with skin exposure assessments? Perhaps they should consider what Einstein once said: “Not everything that can be measured counts, and not everything that counts can be measured”!
My take on this is that while it is certainly more difficult to measure or estimate dermal exposure (compared to inhalation), I believe that some attempt at quantification of dermal exposure is possible.  Dermal penetration modeling, which has been around for some time, is one way of getting a handle on dermal skin exposure potential.    Wil tenBerge has been a pioneer in putting together and sharing useful tools for the assessment of dermal exposure from skin contact with liquids and from skin contact with airborne vapors.   The latest has been his collaboration with Danial Drolet and Rosalie Tibaldi to fashion IH SkinPerm  (see   

Dr. ten Berges previous work on this subject has been freely available for many years on his web site:

Theses tools allow for the estimation (albeit currently unrefined) of how much of a dermally available substance might be absorbed into the body.   A previous blog here highlights the work of Dr. Deborah Lander in evaluating the uncertainty around these models.   Check it out at as the July 7 2014 blog:   Dr. Langer reports  “ that 27% of the model predictions were within a factor of 2,  73% where within a factor of 10 and all of them were within a factor of 30 fold. “  Clearly, 30 is a relatively large factor but my sense is that it can be significantly, if not dramatically, brought down by future experimental data  sets in which the consistency of the quality of the experimental data are carefully monitored and assured.  

The point of all this is that some quantification of dermal exposure is possible today given the details of the exposed skin area and duration of exposure.   If we are dealing with systemic toxic effect then we can estimate systemic dose.   Inhalation OELs can be converted to dermal OELs to make the comparison. If we are dealing with irritation or Type IV contact allergy as the primary response of concern then we are focused on determining the worst case amount per cm2 of exposure.  In my previous work we establish working mg/cm2/day exposure limits for contact allergens.  Thus, both primary types of dermal exposure are subject to quantitative estimates.  We should not fail to look for our “lost keys” in this area that is not “under the street lamp” of inhalation exposure assessment.

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