Exposure to chemicals, which is more important, inhalation or skin?
Published Date: 6th April 2009
In the early days of occupational health, safety and hygiene it was assumed that inhalation exposure was the most significant route for many toxic chemicals to gain access to the body’ 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 gaining access to the body. Also the idea that one might breathe in a toxic substance raises much higher emotive concerns than the idea that some might land on the skin.
So effort tended to be concentrated on preventing inhalation of toxic gases, aerosols, vapours, fumes and dust to protect the workforce and to meet the stringent requirements of the CoSHH regulations. Much research and many studies resulted in clear occupational exposure limits that employers must ensure are not exceeded in the working environment, techniques for measuring airborne exposure, etc. The need for regulatory compliance placed emphasis on inhalation exposure, such that skin exposure tended to be accorded a much lower priority.
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 occupational health exist, there is clear evidence that damage to health due to skin exposure remains, if not the, then certainly 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 U.S. 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 for 10,000 employees, compared with 17,700 respiratory illnesses with a rate of 1.8 illnesses per 10,000 employees.
U.S. Department of Labor, Occupational Safety and Health Authority, Technical Manual, Section II, Chapter 2
In other words skin diseases exceeded respiratory disesease by at a ratio of 2.36:1!
Similarly, in a study by dermatologists in Denmark, the significance of skin disease is clear.
| Principal diagnosis | Compensation claims |
Skin diseases (36%) |
2,853 1,640 791 320 278 2078 |
Total |
7960 |
Halkier-Sorenson C, Occupational skin diseases, a case study from Denmark, Contact Dermatitis, 1998, 39, 71-78 |
|
And from the European Agency for Safety and Health at Work, Fact Sheet no. 40:
“Occupational skin diseases are estimated to cost the EU €600,000,000 each year, resulting in around 3 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 keep 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 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 consider each in isolation.
The consequences of skin uptake can be every bit as serious as for inhalation, as the case of Prof. Karen Wetterhahn demonstrates. A minute exposure to dimethyl mercury on her gloved hand resulted in body 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 of 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 health of workers due to chemical exposure started to devote more time to the issue of skin exposure and its consequences.
Unfortunately, the way in which such exposure occurs can be complex as can the consequences. The reality is that this is actually far more complex than for 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 on the body of the contact, and the consequences that can arise from this.
So in answer to the question in the title, 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.
Subsequent articles will expand on this topic.
This article was provided by Chris Packham of EnviroDerm Services (UK) Ltd. EnviroDerm are a specialist consultancy training provider in the fields of risk assessment, risk management, skin care and skin management. EnviroDerm have a wealth of knowledge and experience that they share brilliantly within their course presentation.