Allergens and Climate Change

Impact of climate change on occupational allergies and infectious diseases

As a national occupational health institute our aim is to focus on emerging threats such as climate change and how it impacts on workers’ health. Dry (El Nino) and wet (La Nina) weather patterns as a result of climate change has and will continue to impact on the environment and consequently on occupational health.

The effects of heat stress and rising CO2 levels may be more obvious ones however it also has an impact on occupational allergies and infectious diseases in several ways. We have categorised the impacts into three priority areas: bioaerosols, occupational allergies, waterborne and vector borne pathogens.


The main factors that change the risk of diseases associated with extreme weather events are the type and location of occupational activity and duration of exposure. Response workers who handle environmental emergencies for example healthcare workers and emergency responders are at greater risk of exposure to the biological hazards associated with sudden, extreme weather events (e.g. moulds, biological agents, microbial byproducts and faecal matter during flooding). Water damaged buildings from rain or floods can lead to mould growth causing allergic, infectious and toxic effects. Severe weather patterns can also affect microbial indoor air quality in buildings. The use of aircons for comfortable indoor air environment during hot or warm humid climates can be a source of bacterial and mould exposure as well. Furthermore, a lack of mechanically ventilated systems where natural ventilation cannot adequately dilute the air in modern crowded buildings due to increasing energy cost to condition (heat, cool, dehumidify) could lead to increased levels of infectious agents (e.g. MTB). Workers in modern buildings without outdoor air ventilation are at increased risk of acquiring TB.

Occupational allergies

Workers especially those who work outdoors may be exposed to increase levels or different types of allergens. Increasing temperatures and CO2 levels promote earlier flowering periods, lengthen pollen seasons, increase the quantities of allergens produced, intensify allergenicity, and change distribution areas and concentration of pollens and other aeroallergen (moulds, spores, and mycotoxins). Distribution of insects, especially allergenic ones such as wasps and fire ants have been shown to increase with increase in temperatures. The effects of exposure to pollens and other airborne allergens in the workplace could translate into an increase in occupational respiratory diseases such as asthma and allergic rhinitis. The components of air pollution interact with the allergens transported by pollen grains and could therefore increase the risks of atopic sensitivity and aggravate symptoms in already-sensitized individuals. Workers in industries where jobs are performed outdoors over long periods of time and require intense physical effort, have a greater potential of exposure to aeroallergens, given the increase in the workers’ respiratory flow and the duration of their exposure. These changes may affect worker sensitivities to these allergens particularly in the agriculture sector. Due to dry weather conditions certain products such as wheat and maize are imported from other countries and workers in the milling companies may be exposed to different types of allergens as a result.

Depletion of the stratospheric ozone can result in greater levels of sunburn, skin cancer & enhanced phototoxicity and photosensitivity reactions. These occur in individuals taking certain medications (diuretics, some antibiotics, and oral contraceptives) and using sun screens when working outdoors e.g. farmers, fishermen and workers in construction, road maintenance, landscaping, and horticulture sectors, as well as lifeguards. Heat stress also impacts on the hydration levels of the skin. The less hydrated the skin is the more sensitive it is to irritants in the workplace possible leading to irritant contact dermatitis. The NIOH skin clinic can perform measurements of the trans-epidermal water loss of the skin. Many outdoor workers may be affected and some are particularly vulnerable in remote and hot parts of the country.

Waterborne and vector borne pathogens

Waterborne diseases are caused by a variety of microorganisms and biotoxins which lead to devastating illnesses such as cholera, schistosomiasis and other gastrointestinal problems. Outbreaks of waterborne diseases often occur after a severe precipitation event (e.g. rainfall, snowfall). These events could result in elevated waterborne disease burden. Climate change is likely to increase diarrheal disease incidence worldwide, and extreme weather conditions may also complicate already inadequate prevention efforts. Although the South Africa has prevention and treatment strategies for waterborne diseases, however the disease prevalence is fairly low possibly due to underreporting, lack of standardised diagnostic approaches and the understanding of the impact of climate change on these diseases is not well established.

The prevalence of vector-borne and zoonotic diseases could increase, according to predictions made in connection with climate change. Higher temperatures would change incubation rates, transmission seasons, and geographic distributions of vector insects (ticks and mosquitoes) and disease-carrying animals; and the rise in temperatures would facilitate the development or introduction of new pathogens or disease vectors in livestock. This is likely to the incidence of infectious diseases and the appearance of new vector-borne diseases. Environmental emergency responders, entomologists, and people who perform necropsies on animals, or who handle possibly infected tissues or fluids are also at risk.

Gaps and future research

  • Through health risk assessments and intervention studies we can bring potential occupational health threats to the attention of policy makers early and help inform policies to reduce the adverse impacts of climate change.
  • Assess current and future risks related to aeroallergens and microbial diseases
  • Assess skin dehydration and photosensitivity in outdoor workers during extreme heat episodes
  • Evaluating and monitoring exposures and health risks of hazardous biological contaminants including allergens likely to be increasingly released due to climate change and its affect on workers health
  • Improving understanding of harmful microbial blooms as well as the biotoxins in water distributions systems and potential health affects to workers
  • Impact of reuse of water storage tanks due to drought conditions (leaching of chemicals)

Services we offer

  • Preparing tests to diagnose new exposures including allergens and conduct indoor air assessments
  • Conduct awareness campaigns to make workers and health professionals aware of the effects on climate on their health
  • Develop measures for raising awareness and informing workplaces (workers and employers) of the potential disease risks associated with climate change


Impacts of Climate Change on Occupational Health and Safety Studies and Research Projects REPORT R-775


Fourie A, Kirsten Z, Matuka O, Ratshikhopha E, Singh T