In the early days of occupational health (OH) safety and hygiene it was assumed that inhalation exposure was the most significant way for many toxic chemicals to enter the body’s internal organs and systems. It was also recognised that the surface area of the gas exchange region of the lung was extremely large – much larger than the surface area of the skin.
Furthermore, the skin was considered a relatively impermeable barrier, preventing chemicals from getting into the body. The idea that one might inhale a toxic substance raises far more concerns than the thought that some might land on the skin.
So effort tended to be concentrated on preventing the inhalation of toxic gases, aerosols, vapours, fumes and dust. Much research and many studies resulted in clear occupational exposure limits that employers must ensure are not exceeded in the working environment, and techniques for measuring airborne chemical exposure. The need for regulatory compliance placed emphasis on inhalation exposure, so that skin exposure tended to be given a much lower priority.
But does this really reflect present day reality? If one studies the statistical and epidemiological evidence that now exists, then some interesting facts come to light. In those countries where effective data collection on the causes of OH exists, there is clear evidence that damage to health due to skin exposure is one of the most significant factors.
Let’s take a look at some of the evidence. Both the number of cases and the rate of skin diseases in the US exceed 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 with 17,7000 respiratory illnesses with a rate of 1.8 illnesses per 10,000 employees.1 In other words, skin diseases exceeded respiratory disease by at a ratio of 2.36:1.
Similarly, in a study by dermatologists in Denmark, the significance of skin disease is clear (see table below). And from the European Agency for Safety and Health at Work, Fact Sheet no. 40 states: “Occupational skin diseases are estimated to cost the EU €600m (£518m) each year, resulting in around three million lost working days. They affect virtually all industry and business sectors and force many workers to change jobs.”
Note that these statistics relate only to the incidence and prevalence of occupational skin disease. There is almost no data on the contribution that skin contact and skin penetration plays in the development of systemic disorders. However, what evidence there is indicates that this has to be significant. With certain chemicals, skin contact and uptake is almost certainly at least, if not more, significant than uptake due to inhalation.
We need to bear in mind that it is the dose that reaches the target organ that is critical for the potential systemic effect, irrespective of the route of the uptake. Thus, when considering systemic effects, we must take the sum of the three routes of uptake (inhalation, ingestion and dermal) as our exposure, rather than considering each in isolation.
The consequences of skin uptake can be every bit as serious as inhalation, as the case of professor Karen Wetterhahn demonstrates. A minute exposure to dimethyl mercury on her gloved hand resulted in uptake (due to permeation through the glove) and her untimely death several months later.
Furthermore, it is possible for airborne exposure of the skin – for example, the face – to result in contact dermatitis. Airborne contact dermatitis has been well-documented in scientific literature, and it has been shown that in someone already sensitised, it is possible for a reaction to occur at below the legally defined inhalation exposure limit. So perhaps it is time that those concerned with health and safety and the prevention of damage to the health of workers due to chemical exposure started to devote more time to the issue of skin exposure and its consequences.
Unfortunately, the way such exposure occurs can be complex, as can the consequences. It is actually far more complex than inhalation exposure, and requires a considerable knowledge of how the skin interacts with the workplace environment, how the skin reacts to contact with chemicals, the nature, extent and location of the bodily contact, and the consequences that can arise from this.
All three routes of exposure are important, the relative importance being determined by the chemical and the nature of the exposure. In many cases relative importance will be irrelevant, as it is the total exposure that will determine the potential for damage to health.
Chris Packham is a partner at EnviroDerm Services (UK)
1 US Department of Labor, Occupational Safety and Health Authority, Technical Manual, section II, chapter 2
Compensation claims in Denmark
|Prinicpal diagnosis||Copensation claims|
Respiratory system disorders
Circulatory system disorders
Source: C Halkier-Sorenson, Occupational skin diseases, a case study from Denmark, Contact Dermatitis, 1998, 39, 71-78