In the 1960s, hay fever affected around four per cent of the population. In the 1990s it affected almost 20 per cent ? one in five of the population. Many allergic diseases have increased at the same rate as hay fever, such as atopic eczema and asthma. The cost of admitting asthmatics to hospital is high and partly relates to less than optimal management of the condition but also the increase in numbers of asthmatic subjects thus making asthma "a significant problem", according to the National Asthma Campaign.

The prevalence of the condition continues to rise, and in the UK an estimated eight million people are diagnosed as having asthma, with five million people receiving treatment. The cost to the NHS is more than £850 million a year, and yet there are many people with asthma for whom available care and medication are not adequately relieving symptoms.

Household allergens and airborne pollens and moulds are the culprits for a significant proportion of asthmatics, but the work place is now becoming increasingly recognised as a cause of asthma.

Work related asthma

The 1995 Self-reported Work-related Illness survey estimated that there were 151,000 people with asthma symptoms that they believed to be work-related. An estimated 797 cases of occupational asthma were seen for the first time by occupational and chest physicians who reported to the SWORD/OPRA surveillance schemes in 2000, bringing the average incidence over the three years 1998-2000 to 911, or around three cases per 100,000 workers per annum.

Over half the cases reported to SWORD in the three years 1998-2000 came from the manufacturing sector, with the highest rates in the production of food and beverages and of motor vehicles, both of which had rates of over six times the national average, says the HSC.

"Reducing cases of occupational asthma by preventing or controlling exposure to substances that can cause the disease. The Health and Safety Commission has set a target to reduce asthma caused by substances at work by 30 per cent by 2010," reported the HSE in March last year.

The USA's Occupational Health and Safety Administration (OSHA) estimates that approximately 11 million workers in a wide range of industries and occupations are potentially exposed "to at least one of the more than 200 agents known to be associated with the development of occupational asthma. OSHA has few specific standards that have been designed to protect employees from the risk of this disease and little national attention has been devoted to this issue. OSHA is developing an action plan to reduce worker exposure to this hazard but is not initiating rulemaking at this time."

Occupational factors have been associated with up to 15 per cent of the disabling asthma cases in the United States. The OSHA estimates that "11 million American workers are potentially exposed to materials that can produce occupational asthma".

Occupational exposure to enzymes

The prevalence of sensitization to enzymes assessed by skin prick testing, according to Markku Vanhanen of the Finnish Institute of Occupational Health, was 7.8 per cent in the bakeries, 4.8 per cent in the flour mill and 2.7 per cent in the rye crisp factory. "When the office personnel were excluded," he reported in 2001, "the figures were 8.4 per cent, 5.3 per cent and three per cent, respectively. In the animal feed industry the corresponding prevalences were 4.6 per cent and 7.1 per cent, and in the detergent industry 11.8 per cent and 22.5 per cent. In the biotechnical research laboratory 11.7 per cent of the workers and in the biotechnical plant 12.6 per cent of the workers were sensitized. In the category of research, laboratory and enzyme manufacturing work, the rates were 12.6 per cent and 15.4 per cent, respectively."