Irritants and allergens

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Jeroen Terwoert,TNO


Irritants – in this article to be understood as being chemical irritants – are substances that may cause injuries to the skin, the eyes or the airways after a single exposure. These injuries may range from small, initially invisible injuries after exposure to weak irritants up to chemical burns after exposure to very strong irritants (i.e. corrosive substances). Prolonged or repeated exposure to weak irritants or a single exposure to stronger irritants may result in lasting health effects such as (irritative) eczema or asthma. Irritants are present in very many sectors and occupations. Irritants and the products containing them may be identified by means of their classification and labelling Labelling of chemicals as well as by using various existing lists. Prevention should include combinations of measures at source, technical and organisational measures, personal protection and hygiene, and early warning.

What are irritants?

Irritants are substances that may cause injuries to the skin, the eyes or airways after a single exposure. These injuries may range from small, initially invisible injuries after exposure to weak irritants up to chemical burns after exposure to very strong irritants (i.e. corrosive substances). In most cases, no lasting health effects will occur after exposure to weak irritants if the exposure is restricted to a single event. However, prolonged or repeated exposure to even weak irritants may result in lasting health effects such as (irritant) eczema or asthma. Irritants are omnipresent in many sectors and occupations. Well-known examples of irritants are:

  • soaps or detergents in cleaning products
  • acids
  • solvents
  • wood dust
  • welding fume

Even water should be regarded as a weak irritant. Prolonged or frequent contact of the skin with water may cause contact dermatitis (eczema).

Health effects

The health effects that irritants cause may force workers to leave their profession. Irritants may also aggravate pre-existing complaints. The workers’ skin as well as the airways and eyes may be affected.

Effects to the skin

Initial acute effects of irritants to the skin may include a prickling sense or rashes (redness). The most significant lasting dermal health effect of irritants is contact dermatitis – also called ‘eczema’. This is an inflammation of the skin which may result in rashes, itch or pain, nodules, vesicles (blisters), scaling, thickened skin and in severe cases fissures. Relatively strong irritants may cause acute irritant contact dermatitis after a single or only a few subsequent exposures. Weak irritants, including water (‘wet work’), may cause a chronic cumulative contact dermatitis when the skin is not allowed sufficient time for recovery from the successive series of small injuries (Fig. 1). Generally, the symptoms of irritant contact dermatitis are quite similar to those of allergic contact dermatitis, which is caused by occupational allergens Occupational allergens. Treatment of contact dermatitis is difficult, which is why it often develops into a chronic skin condition. Eczema may make workers feel insecure and limit social interactions, as well as the performance of manual tasks.

Figure 1: Development of a chronic, cumulative contact dermatitis after repeated exposures to weak irritants


Effects to the airways

Acute effects of irritants to the airways may include a prickling nose or throat, and cough. Irritants may also cause odour nuisance, but not all odorous substances are irritants. However, asthma patients sometimes report that certain odours, even in the smallest amounts, may trigger an attack (CCOH, 2011). The most significant lasting effect of irritants to the airways includes occupational asthma, chronic obstructive pulmonary disease (COPD), rhinitis and toxic lung edema.

Asthma is a disease of the airways, leading to periodic narrowing of the airways, and to an increased sensitivity to all kinds of non-specific stimuli.

Symptoms of asthma include difficulty in breathing, tightness of chest and cough. Asthma is a serious disease that may be life-threatening. Asthma may be related to work in two ways:

  • pre-existing asthma that is aggravated by exposures at the workplace, such as irritants or other stimuli;
  • ‘true’ occupational asthma: asthma that is caused by exposures at the workplace.

In most cases, occupational asthma is caused by allergens Occupational allergens. However, single or repeated high exposures to strongly irritating substances (e.g. chlorine, ammonium) may cause a specific type of asthma called reactive airways dysfunction syndrome (RADS).

COPD (Chronic Obstructive Pulmonary Disease) refers to two diseases: chronic bronchitis (an inflammation) and emphysema, the latter involving a reduction of the elasticity of the lung tissue. Both conditions result in chronic cough and shortness of breath which are irreversible, and eventually disabling. The major cause of COPD is smoking (including passive smoking), but other irritants may be the cause as well, or may aggravate the complaints. The WHO has estimated that COPD as a single cause of death shares 4th and 5th places with HIV/AIDS (after coronary heart disease, cerebrovascular disease and acute respiratory infection). Furthermore, the WHO estimates that in 2000, 2.74 million people died of COPD worldwide (COPD International, 2004).

Rhinitis is an inflammation of the nose, which may be caused by irritants. Rhinitis often precedes the development of allergic asthma, e.g. in farmers.

Toxic lung edema is an accumulation of fluid in the lungs.It leads to impaired gas exchange and may cause respiratory failure. Lung edema may be caused by poorly water-soluble irritants such as mineral oil mists (e.g. cutting fluids). This illness may be acutely life-threatening.

Effects to the eyes

Exposure of the eyes to irritants may cause irritation (redness, pain) and in more severe cases conjunctivitis (‘pink eye’); an inflammation of the clear membrane covering the white part of the eye and interior lining of the eyelids (Segre, 2011).

Professions at risk

Several thousands of irritants are known. Practically everybody gets into contact with irritants, either at work or at home, e.g. as a result of using cleaning products or cosmetics. Exposure to irritants may occur in very many sectors and in many different occupations. Some major professions at risk are indicated in tables 1 & 2.

Table 1: Professions at risk of skin effects (contact dermatitis caused by irritants


Table 2: Professions at risk of airway effects (COPD, asthma, rhinitis) caused by irritants


Risk assessment

The employer should describe potential risks caused by irritants in the obligatory risk assessment. First of all, irritants have to be recognised. Subsequently, risk assessment tools and monitoring may be applied.

Recognising irritants

Irritants at the workplace may be recognised by means of their classification and labelling Labelling of chemicals or, if that is not applicable, by means of available lists of irritants.

Table 3 provides the hazard symbols and risk phrases (R-phrases) or hazard-statements (H-statements) by which irritants may be recognised on the labels or in the safety data sheets (SDS) of substances or products.

Table 3: Classification and labelling of irritants Hazard Symbols


In addition to the label and SDS it may be convenient to consult one or more existing lists of irritants at the workplace. These include substances that may be generated in certain processes instead of being purchased, such as welding fume, diesel motor exhaust, wood dust and glass wool fibres. Such lists can be found for example in publications of EU-OSHA and at the skin at work website of HSE (De Craecker, 2008; Chew & Maibach, 2003; HSE, 2011a).

Risk assessment tools and monitoring

As soon as the potential irritants at the workplace have been identified one may proceed with exposure assessment and risk assessment using one of the available risk assessment tools. Well-known risk assessment tools include for example COSHH-Essentials in the UK, the German EMKG and Stoffenmanager (Dutch and English versions). These have been described in the articles on risk management tools and/or monitoring at the workplace.

In case of exposure by inhalation, the exposure may be assessed against an available Occupational Exposure Limit (OEL) Occupational exposure limit values. In order to establish the appropriate OEL, organisations need to agree upon the types of toxicological end points that are sufficiently important to protect against (e.g. transient eye irritation, enzyme induction or other reversible effects). This is particularly true for sensory irritants. These conditions should also be taken into account when setting preventive measures, particularly when there are several irritants used at workplaces or when there are workers with a particular sensitivity or precondition. The short term exposure limits are used for substances for which short term peaks of exposure could result in serious health effects—for example, respiratory irritants such as chlorine. .OELs for local effects to the skin do not exist. However, the general rule should be to limit skin exposure to irritants as much as possible.


The European Framework Directive on Safety and Health at Work 89/391/EEC Legislation requires that employers assess hazards and risks at the workplace and take measures to control exposure where needed. There are no specific regulations to the group of ‘‘irritants’’ as a whole. However, several EU Member States (e.g. Germany, Netherlands) have made specific regulations that cover the prevention of occupational skin disease, or the prevention of skin and airway disease in specific sectors, such as the hairdressing trade (Safehair, 2010).


The European Framework Directive on Safety and Health at Work (89/391/EC) and the chemical agents directive (98/24/EC) prescribe a hierarchy of control measures. Preferably, measures to control exposure and to prevent health effects caused by substances should be taken at source. If that is not possible, one may take technical or organisational measures or, as a last resort, use personal protective equipment (PPE) Protective clothing against chemical and biological hazards. Some examples that are specific to irritants are mentioned below.

Measures at source

Employers may try to eliminate the use of irritants, i.e. to make the use of irritants superfluous. E.g., upholsterers may install carpets on stairs by means of double-sided tape and clamps instead of adhesives. Medical equipment may be sterilised by heating instead of using disinfectants. By means of careful process design and clean delivery of metal parts, manufacturers of various metal objects (e.g. inner walls or trailers) have been able to eliminate certain cleaning and degreasing steps form the process that involved manual handling of aggressive solvents.

One may also try to substitute irritants by less harmful substances. One example is the use of less volatile hardeners (amines) for epoxy resins, which will reduce inhalation. In the healthcare sector, the substitution of water and soap for hand cleaning by alcohol has been promoted, as the use alcohol has been shown to reduce the risk of contact dermatitis.

In some case, the supplier may adapt the form or packaging of the product. E.g., less dusty (coarser) hair-whitening powder, or a water-soluble packaging for powders that does not have to be opened. In cattle or poultry breeding, powder-formed feed may be substituted by pellets.

Finally, the process may be adapted. One may for instance cut glass wool insulation mats, instead of sawing them. This largely prevents the release of fibres. In road marking, thermoplastic materials may be sprayed, but also poured. Similarly, strong acids that are sometimes used in the cleaning of facades may be sprayed, brushed or poured. Careful emptying bags with e.g. wheat flour or other powder-like materials, and a reduced dropping-height, may largely reduce the formation of airborne dusts.

Technical measures

General ventilation and local exhaust ventilation (LEV) may be effective in case of airway irritants. Examples include spraying booths for (e.g.) isocyanate-containing coatings, soldering irons with integrated LEV on the tool, wood sanding machines with integrated LEV, and working tables with downdraft LEV for nail technicians.

If automation is not possible, specific tools and equipment may still reduce exposure, such as closed mixing vessels for 2-pack products, dispensers for volatile degreasing agents and spraying guns that reduce ‘overspray’ (e.g. High Volume Low Pressure or Air mix spray guns). In floor coating, rollers on a long stem may be used, in order to reduce both inhalation of vapours and dermal exposure.

Organisational measures

When ‘wet work’ is common, job rotation may prevent skin disease, e.g. among hairdressers or nurses. Separation of certain activities, and restricted access, may reduce exposure as well. The hairdressing trade for example, has defined guidelines for the establishment of separated areas for mixing hair colourants etc. (Safehair, 2010).

In meat processing factories, cleaning the production facilities only starts after all other workers have left. Thus, no unprotected workers are exposed to the strong acid or lye cleaning agents, that are usually sprayed onto working surfaces.

Personal protective equipment (PPE)

PPE Protective clothing against chemical and biological hazardsmay only be used when other measures are not sufficiently effective or not possible. One may consult the SDS in order to select the proper PPE. In order to prevent inhalation of solid irritants, filtering facepieces may be sufficient in less demanding cases. Depending on the specific substance and process, more advanced options including full-face air-supplied respirators may be needed. The use of respirators may be too burdensome for workers that already suffer from asthma.

Regarding skin protection: consult the SDS in order to select proper gloves. In any case, leather, cotton and polyethylene gloves are generally not suitable, just like gloves that contain allergens, such as latex. Furthermore, remind the following:

  • Consult the SDS or the product information of the glove, for the maximum time of use for the irritating substance(s) in question.
  • Preferably, use disposable gloves and use them only once:
    • Gloves may get contaminated inside when taking them of or putting them on;
    • The skin may get contaminated when taking gloves off or putting them on.
  • When the gloves are not used, hazardous substances will continue to penetrate through the glove, i.e. working breaks should be counted in the time of use.
  • Never put on gloves when the hands or the gloves are wet or contaminated.
  • Do not use moisture-tight gloves longer as necessarily needed; the hands may get wet as a result of perspiration within 10 minutes already, which may lead to contact dermatitis.
  • Prevent the effect of moisture by perspiration by using cotton inner gloves.

Skin care

It is advisable to use a skin care cream before work starts, every time after washing the hands, and after work. Draw up a skin protection plan, within the framework of the risk inventory and evaluation, which includes measures and instructions for:

  • skin protection before work;
  • skin cleansing during and after work;
  • skin care after work.

In the skin protection plan, take into account:

  • type of contamination, i.e. oily, greasy or strongly clinging such as lacquer, resins, adhesives;
  • moist and wet working areas: metal working fluids, water, washing and cleansing solutions;
  • skin protection when wearing gloves;
  • protection from UV radiation when welding and working under strong sunlight.

Early warning and health monitoring

Early detection of skin abnormalities or airway complaints may prevent the development of more severe complaints such as contact dermatitis, asthma or COPD. One may use:

  • Standardised questionnaires or interviews;
  • Clinical investigations of the airways (lung function tests) or the skin (by the occupational physician, dermatologist or lung specialist).

In order to facilitate early detection of skin disease, so-called ‘pictionnaire’ questionnaires have been developed, which use photos of affected skin (Coenraads et al., 2005).

After finding cases of skin or airway disease, the effectiveness of control measures in place should be evaluated again. Reporting schemes within the company – in addition to any reporting obligation to national occupational disease registries – may increase the companies’ capacity to trace defects in the risk management measures in place.

Good Practice

Examples of good practice in relation to preventing either skin disease or airway disease caused by irritants (often also allergens) have been published by the EU-project Safehair (hairdressers) and the HSE (Safehair, 2010; HSE, 2009), and in Spee, 2006.


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