3.2. Skin corrosion/irritation

3.2.1.1.

Skin corrosion means the production of irreversible damage to the skin; namely, visible necrosis through the epidermis and into the dermis occurring after exposure to a substance or mixture.

Skin irritation means the production of reversible damage to the skin occurring after exposure to a substance or mixture.

3.2.1.2.

In a tiered approach, emphasis shall be placed upon existing human data, followed by existing animal data, followed by in vitro data and then other sources of information. Classification results directly when the data satisfy the criteria. In some cases, classification of a substance or a mixture is made on the basis of the weight of evidence within a tier. In a total weight of evidence approach all available information bearing on the determination of skin corrosion/irritation is considered together, including the results of appropriate validated in vitro tests, relevant animal data, and human data such as epidemiological and clinical studies and well-documented case reports and observations (see Annex I, Part 1, Sections 1.1.1.3, 1.1.1.4 and 1.1.1.5).

3.2.2.2.1.

A tiered approach to the evaluation of initial information shall be considered, where applicable, recognising that not all elements may be relevant.

3.2.2.2.2.

Existing human and animal data including information from single or repeated exposure shall be the first line of evaluation, as they give information directly relevant to effects on the skin.

3.2.2.2.3.

Acute dermal toxicity data may be used for classification. If a substance is highly toxic by the dermal route, a skin corrosion/irritation study is not practicable since the amount of test substance to be applied considerably exceeds the toxic dose and, consequently, results in the death of the animals. When observations are made of skin corrosion/irritation in acute toxicity studies and are observed up through the limit dose, these data may be used for classification, provided that the dilutions used and species tested are equivalent. Solid substances (powders) may become corrosive or irritant when moistened or in contact with moist skin or mucous membranes.

3.2.2.2.4.

In vitro alternatives that have been validated and accepted shall be used to make classification decisions.

3.2.2.2.5.

Likewise, pH extremes like ≤ 2 and ≥ 11,5 may indicate the potential to cause skin effects, especially when associated with significant acid/alkaline reserve (buffering capacity). Generally, such substances are expected to produce significant effects on the skin. In the absence of any other information, a substance is considered as corrosive to skin (Skin Corrosion Category 1) if it has a pH ≤ 2 or a pH ≥ 11,5. However, if consideration of acid/alkaline reserve suggests the substance may not be corrosive despite the low or high pH value, this needs to be confirmed by other data, preferably by data from an appropriate validated in vitro test.

3.2.2.2.6.

In some cases, sufficient information may be available from structurally related substances to make classification decisions.

3.2.2.2.7.

The tiered approach provides guidance on how to organize existing information on a substance and to make a weight of evidence decision about hazard assessment and hazard classification.

Although information might be gained from the evaluation of single parameters within a tier (see Section 3.2.2.2.1.), consideration shall be given to the totality of existing information and making an overall weight of evidence determination. This is especially true when there is conflict in information available on some parameters.

3.2.3.1.1.

The mixture shall be classified using the criteria for substances, taking into account the tiered approach to evaluate data for this hazard class.

3.2.3.1.2.

When considering testing of the mixture, classifiers are encouraged to use a tiered weight of evidence approach as included in the criteria for classification of substances for skin corrosion and irritation (Sections 3.2.1.2 and 3.2.2.2), to help ensure an accurate classification as well as to avoid unnecessary animal testing. In the absence of any other information, a mixture is considered corrosive to skin (Skin Corrosion Category 1) if it has a pH ≤ 2 or a pH ≥ 11,5. However, if consideration of acid/alkaline reserve suggests the mixture may not be corrosive despite the low or high pH value, this needs to be confirmed by other data, preferably by data from an appropriate validated in vitro test.

3.2.3.2.1.

Where the mixture itself has not been tested to determine its skin corrosion/irritation potential, but there are sufficient data on the individual ingredients and similar tested mixtures to adequately characterise the hazards of the mixture, these data shall be used in accordance with the bridging rules set out in Section 1.1.3.

3.2.3.3.1.

In order to make use of all available data for purposes of classifying the skin corrosion/irritation hazards of mixtures, the following assumption has been made and is applied where appropriate in the tiered approach:

The ‘relevant ingredients’ of a mixture are those which are present in concentrations ≥ 1 % (w/w for solids, liquids, dusts, mists and vapours and v/v for gases), unless there is a presumption (e.g., in the case of skin corrosive ingredients) that an ingredient present at a concentration < 1 % can still be relevant for classifying the mixture for skin corrosion/irritation.

3.2.3.3.2.

In general, the approach to classification of mixtures as corrosive or irritant to skin when data are available on the ingredients, but not on the mixture as a whole, is based on the theory of additivity, such that each skin corrosive or skin irritant ingredient contributes to the overall skin corrosive or skin irritant properties of the mixture in proportion to its potency and concentration. A weighting factor of 10 is used for skin corrosive ingredients when they are present at a concentration below the generic concentration limit for classification with Category 1, but are at a concentration that will contribute to the classification of the mixture as skin irritant. The mixture is classified as corrosive or irritant to skin when the sum of the concentrations of such ingredients exceeds a concentration limit.

3.2.3.3.3.

Table 3.2.3 provides the generic concentration limits to be used to determine if the mixture is considered to be corrosive or irritant to the skin.

3.2.3.3.4.1.

Particular care must be taken when classifying certain types of mixtures containing substances such as acids and bases, inorganic salts, aldehydes, phenols, and surfactants. The approach explained in Sections 3.2.3.3.1 and 3.2.3.3.2 may not be applicable given that many such substances are corrosive or irritant to the skin at concentrations < 1 %.

3.2.3.3.4.2.

For mixtures containing strong acids or bases the pH shall be used as a classification criterion (see Section 3.2.3.1.2) since pH is a better indicator of skin corrosion than the concentration limits in Table 3.2.3.

3.2.3.3.4.3.

A mixture containing ingredients that are corrosive or irritant to the skin and that cannot be classified on the basis of the additivity approach (Table 3.2.3), due to chemical characteristics that make this approach unworkable, shall be classified as Skin Corrosion Category 1 if it contains ≥ 1 % of an ingredient classified as Skin Corrosion or as Skin Irritation (Category 2) when it contains ≥ 3 % of an skin irritant ingredient. Classification of mixtures with ingredients for which the approach in Table 3.2.3 does not apply is summarised in Table 3.2.4.

3.2.3.3.5.

On occasion, reliable data may show that the skin corrosion/irritation hazard of an ingredient will not be evident when present at a level at or above the generic concentration limits mentioned in Tables 3.2.3 and 3.2.4 in Section 3.2.3.3.6. In these cases the mixture shall be classified according to that data (see also Articles 10 and 11). On other occasions, when it is expected that the skin corrosion/irritation hazard of an ingredient is not evident when present at a level at or above the generic concentration limits mentioned in Tables 3.2.3 and 3.2.4, testing of the mixture shall be considered. In those cases the tiered weight of evidence approach shall be applied, as described in Section 3.2.2.2.

3.2.3.3.6.

If there are data showing that (an) ingredient(s) is/are corrosive or irritant to skin at a concentration of < 1 % (skin corrosive) or < 3 % (skin irritant), the mixture shall be classified accordingly.

Note:

The sum of all ingredients of a mixture classified as Skin Corrosion Sub-Category 1A, 1B, or 1C respectively, shall each be ≥ 5 % in order to classify the mixture as either Skin Corrosion Sub-Category 1A, 1B or 1C. If the sum of the ingredients classified as Skin Corrosion Sub-Category 1A is < 5 % but the sum of ingredients classified as Skin Corrosion Sub-Category 1A + 1B is ≥ 5 %, the mixture shall be classified as Skin Corrosion Sub-Category 1B. Similarly, if the sum of ingredients classified as Skin Corrosion Sub-Category 1A + 1B ingredients is < 5 % but the sum of ingredients classified as Sub-Category 1A + 1B + 1C is ≥ 5 % the mixture shall be classified as Skin Corrosion Sub-Category 1C. Where at least one relevant ingredient in a mixture is classified as Category 1 without sub-categorisation, the mixture shall be classified as Category 1 without sub-categorisation if the sum of all ingredients corrosive to skin is ≥ 5 %.

3.2.4.1.

Label elements shall be used for substances or mixtures meeting the criteria for classification in this hazard class in accordance with Table 3.2.5.