In a new study by British researchers, one in six cases of adult-onset asthma was linked to the workplace. Additionally, the illness was strongly associated with 18 different occupations --particularly those that exposed workers to chemicals -- such as cleaning jobs, farming, hairdressing and printing.

A team led by Rebecca Ghosh of Imperial College London studied 7,500 British adults born in 1958. The researchers examined information on the participants' job histories, and asthma and bronchitis symptoms at the ages of 7, 11, 16, 33 and 42. The study participants' sensitivity to allergens and lung power was also assessed at the ages of 42 and 45.

Using the Asthma Specific Job Exposure Matrix, the researchers then calculated the participants' exposure to compounds with a known link to asthma, including respiratory irritants and high-risk agents such as flour, enzymes, cleaning or disinfectant products, metal and metal fumes, and textile production.

The study was published online Jan. 21 in the journal Thorax.

After adjusting for various factors -- including smoking -- the investigators found that jobs were linked to 16 percent of adult-onset asthma cases among the group. While the study found an association, it did not prove that the nature of their occupations caused the onset of asthma.

The study showed those exposed to low-risk agents were 20 percent more likely to develop asthma as an adult. The people exposed to high-risk agents were 53 percent more likely to be diagnosed with the respiratory condition. The participants exposed to both types of agents had a 34 percent greater risk of developing asthma.

The findings suggest jobs involving cleaning or cleaning agents showed the strongest link to adult asthma. Meanwhile, farming more than quadrupled the risk for the condition, hairdressing doubled the risk and printing work tripled the risk.