MoD Health & Safety Handbook 

JSP 375 Vol 2 

5.2 

Allergic:

 This depends upon a sensitisation process with the consequent development of a 

type IV allergy to the causative agent. Causative agents include cosmetics (especially those 

containing dyes), medicaments (especially those containing antibiotics), certain metals (e.g. nickel), 

some plant juices and some types of rubber (especially latex). The sensitisation period is a 

minimum of several days, but may be many years. Subsequent exposure may then result in an 

outbreak of dermatitis occurring after a small delay of hours or days. Damaged skin due to irritant 

dermatitis is more likely to result in positive sensitisation to allergens. 

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For a substance to cause dermatitis, it must be able to penetrate the outer layer of the skin and/or 

change it in some way. Some substances can remove oils and moisture from the outer layer of the skin. 

This reduces the protective action of the skin and increases the ability of substances to enter or infiltrate 

the skin. The part of the body that comes into contact with the substance is also important. The 

penetration of substances varies over different body regions (mainly due to thickness of the skin). For 

example the skin of the face, creases of the elbow and behind the knees are penetrated more easily 

than the skin of the hands. The most resistant part of the body is the soles of the feet. 

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Hereditary factors are probably most important in determining an individual's susceptibility to 

irritants. A history of atopic eczema is particularly important, especially if there are current or recent 

allergy problems. Individuals with a history of hand dermatitis or atopic eczema should, if possible, be 

screened out before employment is offered if the occupation carries significant risk of contact with 

irritants and allergens. 

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Environmental factors also play a significant role. For example, hot, humid workplaces cause 

workers to sweat. Sweat dissolves some types of chemicals increasing their effect on the skin. Working 

where the air humidity is high or where the skin is wet for long periods can also lead to conditions that 

aid the penetration of chemicals into the skin. 

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Friction against the skin can scrape away some of the protecting layer, reducing its protection 

against harmful substances. Likewise, cuts and skin injuries may also allow substances to penetrate the 

skin more easily. Clothes soaked in chemicals may also aid skin penetration by keeping chemicals in 

close proximity to the skin for prolonged periods. Some of the factors contributing to increased skin 

penetration are summarised in Table 1. 

Related to the substance 

Related to the person 

Related to the environment 

Properties of the chemical 

Region of skin (hands, face) 

Temperature 

Solubility 

Condition of skin (cuts, grazes) 

Humidity 

Form: gas, liquid, solid, powder 

Dryness 

Friction 

Concentration 

Sweating 

Contamination and spread 

Duration, frequency and extent of 

Age 

Constantly wet 

contact/exposure 

Genetic background 

PPE unsuitable for task 

Table 1   Factors that may increase penetration of the skin 

PREVENTING OCCUPATIONAL DERMATITIS 

10  The general preventive measures to avoid occupational dermatitis follow the principles of exposure 

control that should ensure a safe system of working in any activity involving harmful substances: 

10.1 

Risk Assessment to identify hazardous substances (especially relevant to skin exposure 

are labels 

corrosive, irritant or sensitising 

under CHIP; also a notation  

sk

  against the entry for the 

substance in EH40 [the HSE annual publication of Occupational exposure limits] although this may 

refer to systemic as well as local effects). 

10.2 

Substitution of a less harmful substance (or in a less harmful form). 

10.3 

Enclosure of the process. 

Leaflet 5 Annex E 

April 2003 

 Page 

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