Additional HSE guidance on asthma can be found on its website. This explains that work-related asthma or asthma made worse by work is broader and includes substances in the workplace that irritate the airways of individuals with pre-existing asthma, including people who have had asthma since childhood. Respiratory irritants may trigger attacks in those with occupational asthma or pre-existing asthma. Examples include chlorine, general dust and even cold air.