Work allergies: the evidence base reviewed

Two new systematic evidence reviews on occupational allergies have been published by the British Occupational Health Research Foundation (BOHRF) addressing a type of occupational ill health that, although rarely life-threatening, represents the biggest single category of work-related disease occurring in western industrialised countries.

Occupational asthma

Occupational asthma (OA), the subject of the first report1, is the most frequently reported occupational respiratory disease in the UK. Occupational factors account for one in six of all asthma cases in people of working age, according to BOHRF. There are two main categories:

  • the irritant-induced occupational complaint, most commonly associated with high-concentration exposures, such as following chemical spills; and

  • sensitiser-induced occupational asthma (SIOA), usually associated with extremely low exposures to certain dusts, vapours or fumes (isocyanates, platinum salts, epoxy resin curing agents, wood dusts, proteolytic enzymes, etc).

Almost 90% of occupational asthma cases are of the allergic, SIOA type, and the BOHRF report does not consider the irritant-induced form of the complaint.

Occupational contact dermatitis and urticaria (OCDU)

Occupational skin disease, the subject of the second BOHRF report, is the second most common occupational disease in the EU after musculoskeletal disorders. Irritant contact dermatitis is more common than allergic contact dermatitis.

Multiplicity of causative agents and mechanisms

In the case of both OA and OCDU, a variety of possible causative physiological mechanisms are involved, making accurate diagnosis difficult and/or time consuming. The BOHRF reports explain that the distinctions between the different disease types are important, particularly in the case of OA, because the implications for occupational health management of the complaints are different in each case.

SIOA was characterised more than 20 years ago and has remained a focus of Health and Safety Executive (HSE) awareness campaigns ever since, such as those aimed at motor vehicle paint sprayers and hairdressers. Steve Coldrick, head of the HSE’s long-latency health risks division, opened a recent London conference held to mark the launch of the BOHRF reports with a description of this activity – part of the HSE’s disease reduction programme that is linked to ambitious targeted reductions in the global burden of occupational ill health and disease.

UK shamefully behind Europe

Baroness Finlay of Llandaff, chair of a House of Lords Scientific and Technical Committee of Enquiry into Allergy that reported in 2006/73, opening the London conference, explained the broader UK healthcare context, noting that there is a significant problem of poorly co-ordinated allergy services in the UK.

Secondary care in the UK health service was “shamefully behind” other European countries in the way that allergy is diagnosed and treated, Finlay said. The Lords committee had visited Germany and noted how effective, multidisciplinary allergy services operated there.

Suggested improvements to UK allergy services will be among the recommendations of a forthcoming report – from a joint committee of the Royal Colleges of Physicians, and Pathologists, respectively.

This will recommend the setting up of “clusters” of relevant specialists – at least one in each regional heath authority – located together to facilitate accurate diagnosis and treatment of asthma without the need for the multiple referrals that currently take place, involving patients being passed from different specialist department to department – from dermatologist, to immunologist, etc – in search of an accurate diagnosis, Finlay said. Such multidisciplinary allergy service centres existed in other European countries and needed to be established in the UK health service.

Updated asthma report

The occupational asthma review is an updated version of BOHRF’s first evidence review on OA published in 2004 that included guidelines adopted by the Finnish government as its national standard. On the strength of that report, the Department of Health in England and Wales introduced two new so-called Read Codes, that prompt GPs with patients of working age presenting with either rhinitis or conjunctivitis (precursors of occupational asthma) to ask what job they do. GPs should then consider the jobs most associated with occupational asthma and arrange for serial peak flow measurement and quickly refer to a specialist. This is the evidence base for practice to give the opportunity to break the cycle of early-stage occupational asthma.

The new asthma report reiterates the recommendation regarding serial peak flow measurement, reminding health professionals that occupational factors account for one in six cases of asthma in people of working age and underlining the importance of early diagnosis, particularly where sensitisers – the most common cause of OA – may be involved.

The occupations most commonly associated with OA are: animal handling, baking and pastry making, hairdressing, paint spraying, welding, nursing, and jobs in food processing and the chemical and timber industries.

New dermatitis report

The new BOHRF report on dermatitis was commissioned on the recommendation of the Lords committee of enquiry into allergy. It is the first systematic evidence review published in any country that covers all employment sectors. Key evidence-based recommendations from this review include the need to avoid the promotion of pre-work creams (barrier creams) and, conversely, to actively promote the use of after-work (conditioning) creams. The report also includes important and practical recommendations about glove use.

Leaflets summarising the conclusions of the BOHRF reports will be available in the near future4: for GPs and practice nurses; occupational health physicians/nurses and safety practitioners; and employers, workers and their representatives.

GPs not yet fully aware

Other presentations on occupational allergies at the London conference covered research on enzyme sensitisation and evidence-based guidelines for employers faced with the dilemma of whether or not it is safe to employ people who report that they have, or have had, asthma.

Also presented were results of BOHRF-funded research on the testing of a BMJ e-learning module designed to influence GP behaviour in implementing evidence-based guidelines. The e-learning module used the original BOHRF guidelines on occupational asthma as a vehicle.

The research results clearly demonstrated the difficulty of “reaching” GPs because nearly half of respondents professed never to have heard of the first BOHRF evidence review, despite BOHRF having sent the summary of the evidence to every GP and practice-based nurse in the UK, via their Local Medical Committees.

Types of occupational asthma

Asthma is a condition of chronic inflammation of the airways, characterised by widespread airflow limitation that is reversible – either spontaneously or with treatment – over short periods of time. Inflammation results in hyper-responsiveness of the airways to many stimuli – eg, cold air, cigarette smoke, exercise and, in the hospital clinic setting, to methacholine and histamine. Symptoms include wheezing, coughing, shortness of breath, and tightness of the chest, often worse at night or in the early morning.

Asthma is common, affecting people of all ages. Adult asthma may be a continuation of childhood asthma, reactivation of quiescent childhood asthma, or new-onset asthma.

Asthma is “work-related” when there is an association between symptoms and work. Work-related asthma includes two distinct categories:

  • work aggravated asthma – pre-existing or coincidental new onset adult asthma which is made worse by non-specific factors in the workplace – eg, cold, dry air, dust and fumes

  • occupational asthma – asthma induced by exposure in the working environment to airborne dusts, vapours or fumes, in those with or without pre-existing asthma.

Occupational asthma can be subdivided into two categories:

  • sensitiser-induced occupational asthma, characterised by a latency period between first exposure to a respiratory sensitiser at work and the development of immunologically mediated symptoms

  • irritant-induced occupational asthma that occurs typically within a few hours of a high-concentration exposure to an irritant gas, fume or vapour at work.

Substances that induce asthma through an allergic mechanism can be divided into high (HMW) and low molecular weight (LMW) agents. HMW agents are usually proteins. While some LMW chemicals are associated with a similar immunological mechanism, for the majority of cases of asthma attributable to LMW chemicals, the type of mechanism is unclear.

For some agents, both immunological and non-immunological mechanisms may be involved.

The term occupational asthma is used throughout the BOHRF report to refer to sensitiser-induced occupational asthma, which accounts for 90% of all occupational asthma.

John Manos is editor of Health Protection Report.


1 BOHRF. Occupational asthma: prevention, identification and management – systematic review and recommendations (review report), 25 February 2010. Downloadable from:

2 BOHRF. Occupational contact dermatitis and urticaria: systematic review and recommendations (evidence review), March 2010. Downloadable from:

3 House of Lords Select Committee on Science and Technology, 2007. Allergy: Volume 1: report. Downloadable from:

4 Further information:

Comments are closed.