Prevention of irritant contact dermatitis

ARTICLE

Characteristics of prevention in irritant dermatitis

Two kinds of irritant contact dermatitis can roughly be distinguished, acute and chronic irritant dermatitis [1]. Acute irritant contact dermatitis is mostly caused by an accident in an occupational or sometimes in a private environment, where a strong irritant (mostly an acid or an alkaline solution) interacts with the skin. This can be seen, for example, when disinfecting solutions are used incorrectly. The features vary from a little dryness and erythema to severe edema, inflammation and vesiculation. The primary prevention of such accidental acute irritant dermatitis should be the creation of a safe working environment [2]. By contrast, chronic irritant dermatitis is more frequent [3] and is mostly caused by long lasting and repetitive contact of a weak irritant to the skin (Fig. 1). Skin recovery after chronic irritant dermatitis is in general retarded. To a large degree this is caused by the fact that contact with the relevant irritant is mostly insufficiently reduced because habits are not easily changed. The preferred method for avoiding chronic irritant dermatitis is to prevent its establishment: i.e. primary prevention. This review article deals therefore mainly with this topic.

Prevention can be performed by a combination of collective and individual measures [4]. In general, collective measures of prevention are more effective than individual ones, particularly in the prevention of allergic contact dermatitis, where elimination of allergens (by removal of allergens [5] or using allergens in closed systems [6]) leads to a diminishing of allergic contact dermatitis. By contrast, irritant dermatitis is often induced by inadequate individual behavior at work and should, therefore, be more easily prevented by an appropriate behavior [7]. Hence, in irritant contact dermatitis the individual measures of prevention are very important.

To perform primary prevention sufficiently, certain investments have to be made by companies and (to a lesser extent) by the workers. Although in recent decades the safety of the working environment has continuously improved, the essential problem of all health prevention (especially primary prevention) is still that it is not adequately paid for [8, 9]. An individual who is starting his job (or his training) does usually not think of occupational diseases. Even when it is mentioned in his training (or at the work place) the reaction is usually "this does not refer to me, I'm healthy". Individual understanding of prevention is more pronounced after the disease (irritant dermatitis) has occurred. The efforts of individuals are therefore more effective when secondary or tertiary prevention is performed. On the other hand, it is very difficult to change a behavior pattern which has become a matter of routine for years. A nurse who has washed her hands 80 times a day will reduce this only with a strong effort of will after she develops problems with her hands. The correct training of a preclinical student nurse is easier to perform than the change of behavior after several years of work.

Prevention of irritant contact dermatitis cannot be viewed separately from allergic contact dermatitis. Irritant dermatitis is a risk factor for the development of an allergic contact dermatitis [10]. There are several reasons:

* the penetration of contact allergens is enhanced when the epidermal barrier is disturbed [11, 12];

* the number of dendritic cells is increased by a disturbed barrier [13, 14];

* during irritant inflammation, haptens can be oxidated by reactive oxygen species, leading to an enhanced sensitization capacity of the hapten [15];

* during irritant inflammation, multiple cytokines are produced, supporting the induction of sensitization and challenge of allergic contact dermatitis [16, 17].

Thus, prevention of irritant dermatitis means simultaneously prevention of allergic contact dermatitis.

The role of the dermatologist

To perform primary prevention, an interactive management of doctors, employers, employees, technicians and workers is required. The dermatologist plays a pivotal role in this process with several assignments [18].

Identification of individuals with a higher risk and advisory service

The identification of individuals with a higher risk of developing an irritant contact dermatitis is not easy because reliable prospective data for such risk persons are scarce. A rather important factor for development of irritant contact dermatitis is the occurrence of hand dermatitis in the case history [19]. Obviously, these individuals may have a skin with a disrupted barrier, or at least a barrier that can be more easily disrupted by irritants. Individuals with an atopic dermatitis (according to the definition of Hanifin & Raika [20]) belong to this risk group, but their susceptibility to irritants is dependent on the severity of their actual skin condition [21]. The atopy score according to Diepgen [22] can give further hints to pinpoint individuals with a higher risk of developing an irritant dermatitis. However, this atopy score should not be overestimated because individuals with a high atopy score but without clinical signs of atopic dermatitis do not react more strongly to irritants such as the anionic detergent sodium lauryl sulfate [23]. Moreover, the prognostic value of the atopy score according to Diepgen for occupational hand eczema is limited [24, 25].

The dermatologist should speak to his young high-risk patients about their career plans. He should explain the possible consequences of choosing a career in a risk occupation as listed in Table I. When a high risk occupation is chosen, the dermatologist should give advice about preventive measures. In each risk occupation there are areas of work where the risk of impairment of the skin is diminished. E.g., nurses with a susceptible skin may switch to areas without direct contact of patients, like quality management or nurse-teaching.

Skin tests

Unfortunately, we have no skin test that can exactly assess the risk of a patient to develop an irritant dermatitis. The time-honored (and still often used) tests according to Burckhardt, the alkali resistance and alkali neutralization test, mostly failed to identify risk groups [26, 27]. Irritant tests contain the following main problems: most of the tests are artificial assays where a short contact (mostly up to 48 hours) of an irritant to the skin is performed [28]. This hardly mimics the reality, but can be standardized sufficiently. By contrast, testing procedures that mimic the reality much better, such as some provocation tests (e.g., washing over 7 days), are time consuming and hardly standardized [29, 30]. The practicability of such repetitive irritation tests for routine examination is poor [31]. A further problem of irritant testing is that the reaction to one irritant cannot predict the reaction to another one [32]. Hence, for divergent irritants, different tests are recommended. The development of modern tests with a better prospective validity is underway at the moment. So far, skin tests are not very helpful in questions concerning prevention.

Identification of irritants

Each profession has its particular range of relevant irritants. These irritants are mostly identified by in vitro or animal testing, as well as in vivo human testing. In recent decades, the improvement of bioengineering methods has enhanced the development of more exact in vivo human testing with lower side-effects [33]. Each individual has defined irritants in his working environment, and the relevant ones must be evaluated. Moreover, the frequency of contact has to be taken into consideration, as well as the type of contact (see below). The dermatologist should make sure that his patient knows the most important irritants and concomitant risk factors.

Prevention by collective measures

All measures performed to prevent irritant contact dermatitis are aiming to reduce the contact of an irritant with the skin or to reduce the irritability of an irritant. Collective measures concern all employees no matter whether or not they have skin problems [34]. Such procedures mostly do not depend on the motivation of individual employees to carry out prevention measures. Therefore they can be very effective and it is recommended that all measures capable of reducing the incidence of irritant dermatitis be put in action.

Skin compatibility of external agents

A substance is an irritant when it has the ability to irritate the skin. This simple statement implies that virtually every agent can function as an irritant. For example, the irritant potential of water is well known, and many high-risk occupations imply an intense contact with water [30, 35]. Rather weak irritants can be very noxious because their danger is mostly underestimated and preventive measures are more likely to be neglected. On the other hand, when the skin irritability of external agents has to be improved, rather strong irritants are of interest. An example of the mitigation of strong irritants can be seen in the case of detergents. Sodium lauryl sulfate was one of the earliest detergents used in skin cleaning products [36, 37]. It is very effective and produces a handsome foam. However, its strong irritancy led to efforts to develop less irritative detergents like sodium laureth sulfate or cocamidopropyl betain (an allergen of increasing interest) [38]. Further improvement has been achieved by the addition of a milder irritant to a strong irritant which reduces the irritancy of the mix [39-41]. This may be an effect of the reduction of the critical micellar concentration of the solution, which lowers the concentration of free detergent monomers. These free monomers are likely to be the most important structures for irritation in a detergent solution [41]. Moreover, several detergents can compete for binding sites on the skin preventing a strong reaction to the most irritant detergent. All of these aspects have led to a decrease of products where sodium lauryl sulfate is used alone, an example of prevention of contact dermatitis by a collective measure. Many similar efforts have led to the development of substances with a lower irritant potential. The systematic replacement of strong irritants by weaker ones is a crucial point in primary prevention of irritant contact dermatitis.

Relevant factors in ICD

The example of water given above shows that not only the substance itself is of relevance. Hence, weak irritants can play a major role in irritant dermatitis when several supporting factors are involved:

* The frequency of contact to irritants is important. The skin needs time to recover after every contact with an irritant [42]. When the frequency of irritant contact is too short, the skin cannot recover any more and the barrier gets worse until a clinically manifest irritant contact dermatitis occurs (Fig. 2) [43]. Decreasing the frequency of contact to an irritant is a pivotal factor in individual measures of prevention (see below) and can often be achieved by appropriate hand washing and hand protection at the working place.

* The duration of the contact as well as the concentration of the irritant are directly connected with the irritation [44]. This means, for example, that one should take only small amounts of detergents for handwashing. The detergent must be rinsed off completely to avoid remnants on the skin.

* The kind of contact is important. An occlusive contact potentiates the effect [45, 46]. Therefore, gloves should be considered with caution. Many employees use gloves in a way that irritants can run into the glove, resulting in an occlusive irritant application.

* The temperature of irritants is relevant. Some chemicals produce a stronger irritation when they are dissolved in a warm solution [47-49].

* Mechanical irritation supports chemical irritation. This is observed when hand cleansers contain mechanical abrasives [50].

* A concomitant action of different irritants may potentiate the irritation in an unforeseeable way [51]. Such compound-irritations have not yet been sufficiently studied.

Prevention by individual measures

As far as preventive action is concerned, it is mostly not necessary for irritants to be avoided completely. A reduction of the duration and frequency of contact is sufficient [34]. This reduction can mostly be achieved by correct use of individual skin protection products like gloves and protective clothing but must be supported by correct training and continuous motivation of the employees. In contrast to the danger of allergic contact dermatitis, individuals are likewise at risk of irritation during their free time. After working in a place where the skin is traumatized with irritants, the burden goes on after arriving at home, where infants and household chores are waiting and gardening has to be done.

Gloves and protection clothing

The use of protective gloves and clothing can be very effective. However, their use is accompanied by several problems [18, 45, 52, 53]:

* A suitable glove must fit very well because non-fitting gloves can lead to dangerous situations, especially during work on machines.

* Gloves can provide an occlusive milieu which is an irritant situation in itself.

* When an irritant gets into the glove, the occlusive milieu leads to an increase in irritation. Therefore, holes and leaks in gloves must be strictly avoided as must the introduction of chemicals into the glove. When cotton gloves are worn under rubber gloves (often worn by individuals with dermatitis who want to avoid the occlusive milieu), these gloves should not go beyond the upper margin of the rubber gloves, because otherwise the cotton gloves would suck the irritant into the occlusive milieu under the rubber glove.

* Gloves have to be chosen carefully with consideration of the working environment as some combinations between glove materials and chemicals are known to be inappropriate. While rubber and latex gloves are usually recommended for medical work, hairdressers need polyethylene gloves, which are impermeable to thioglycolates [54, 55]. Other gloves (ethylene vinyl alcohol copolymer sandwiched between polyethylene) are needed for protection against epoxy resin, methyl methacrylate and other organic compounds [56-58].

* The increasing prevalence of immediate and delayed-type allergy to latex and rubber additives requires additional means: the amount of latex in gloves should be diminished further and latex gloves should be powder-free. Wearing a thin polyethylene glove under the latex glove may prevent reactions in sensitized individuals [59-61].

Skin cleansing

In several professions, like nursing, skin cleansing is a major cause of irritant dermatitis [30]. Individuals in these professions should be informed about the correct methods of hand cleansing, because sometimes even the basics of an appropriate skin cleansing are not known. The frequency of hand washing is a crucial point because the irritant dermatitis is a skin damage caused by cumulative low irritations. The hands should be washed only when it is necessary. In contrast to older findings [62], it is now widely accepted that in medical professions disinfection of the hands with alcoholic solutions is far less irritative and should be preferred [63]. However, many nurses feel burning after using disinfecting solutions for the hands. This is not caused by an irritative effect of the solution, it is rather caused by a disrupted epidermal barrier where the alcoholic solution can penetrate into the skin and cause the burning by reaching sensitive nerves. This disrupted barrier, however, is usually caused by frequent washing of hands. When disinfection is felt as burning, washing is again preferred by these individuals. To avoid such a vicious circle, primary prevention means already showing e.g. student-nurses the correct way of hand cleansing and informing them about the risk of frequent hand washing [62, 64]. Often student-nurses wash their hands very frequently because they do not know exactly when washing is recommended. The choice of an appropriate skin cleanser (normally ordinary liquid/gel-like hand cleansers) is as important as its suitable quantity. The use of heavy duty cleansers is reserved for professions with heavy soiling of the hands, like that of metal workers [65]. Pure solvents for removing soil or paint-remnants on the hands should certainly not be used, as their irritative effect (like lipid-extraction) is extremely strong. A better way of cleaning heavy soil from the hands may be the precleaning with a less irritating oil and by subsequent washing with a normal liquid hand cleanser [66].

Barrier creams/moisturizers

Individuals working in occupations with a higher risk of skin irritation often use barrier creams to protect the skin and moisturizers to aid the regeneration of the skin barrier. Barrier creams, often called "invisible gloves", are usually well accepted by the workers as they are less inconvenient than gloves even if they are not effective to a similar degree. However, Frosch et al. [67, 68] showed that the effectiveness of a barrier cream cannot be predicted by looking at its formulation. Hence, the belief that oil-in-water emulsions are primarily effective against lipophilic irritants, and water-in-oil emulsions do the same against hydrophilic irritants, may be incorrect. Many barrier creams are tested in vitro, but in vivo testing should be preferred to investigate their efficacy as protective agents. Some investigators used a guinea pig model for testing the efficacy of barrier creams [69, 70]. The evaluation methods varied between visual scoring systems, histological findings (skin biopsies) and bioengineering methods (evaporimetry, Laser Doppler velocimetry). Many tests have been performed in humans with repetitive irritations [68], evaluated by visual scores as well as by multiple bioengineering methods (evaporimetry, Laser Doppler velocimetry, chromametry, stratum corneum hydration, sebumetry and measurement of pH). With these techniques various features of barrier creams have been detected. Unfortunately, there is no general rule for the effectiveness of barrier creams. The literature data are conflicting, because of different models for investigation (review [71]). Hence, we need a sufficient standardized interlaboratory study protocol that has to be evaluated in clinical workplace studies. In fact, the protection against various irritants has to be proven for each single irritant [68]. Barrier creams are usually not tested sufficiently in vivo against the most important irritants, and even less against a combination of different irritants. Because there is often more than one irritant present in the working environment [51] and the effect of the barrier cream against these cumulative irritations cannot be predicted, the only feasible method is to try some barrier creams for each individual in his own working environment. It has to be kept in mind that barrier creams may have an irritant potential of their own, so that their use cannot be generally recommended without supervision by a dermatologist.

The use of a moisturizer to aid the regeneration of the skin barrier is widely accepted, even by the affected individuals. When it is noticed that the hands are getting rough and scaling, the use of a moisturizer is usually the first action. This behavior is supported by most dermatologists but its efficacy is hardly proven. Only a few studies with repetitive irritations and subsequent application of a moisturizer have been performed [72]. Usually, a slight improvement was noted at the treated areas, but the effect was not impressive. For more convincing results, further studies, especially under daily working conditions, are needed. As the application of a cream after work in his free time is most convenient for the employee (no interference of the work with the treated hands), the development of a highly effective "after-work-barrier-recovery-cream" would be a major advance in the prevention of irritant skin reactions.

CONCLUSION

Training and motivation

Some collective measures and all individual measures of prevention are rules of conduct that are only effective when they are performed correctly by each individual. Even the barrier cream with the most potential will fail if it is used inadequately. Training is therefore one of the most important measures in the prevention of irritant contact dermatitis [7, 64, 71]. This training should be carried out during job training as well as at regular intervals at the place of work. Knowledge about irritation and irritants (actual irritants in a given working environment) must be increased and especially all the possible means for the individual of prevention (protection by gloves and clothes, barrier creams, correct skin cleansing) should be considered. Practical sessions, like testing of cream-application with a fluorescence technique, are very helpful [73, 74]. With the integration of the individual in such training programs a higher level of awareness can be reached. This experience, rather than anonymous instructive brochures given to the workers, can initiate behavior changes.

Article accepted on 22/11/01

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