Rosin components identified in diapers 

Contact Dermatitis, 34, 176-180 1996

Ann-Therese Karlberg and Kerstin Magnusson
Division of Occupational Dermatology, National Institute of Occupational Health, Solna, Sweden

As part of the investigation of sources of exposure to rosin allergens, disposable diapers (napkins) common on the Swedish market were analyzed, using gas chromatography, to detect the main rosin compounds. Rosin components were detected in all diapers, the highest amounts in those from the 2 major producers. In these diapers, more rosin was found in the top layer, which is in close contact with the skin, than in the fluff. Despite the possibly minimal risk of induction of sensitization to rosin allergens in diapers, there is a real risk of elicitation of dermatitis in sensitive individuals, especially since penetration is enhanced by occlusion and irritation. Such material is not only used for infant diapers, but also for adult incontinence products and feminine hygiene products.

Key words: chemical analysis; colophony; contact allergy; diaper; napkin; paper; rosin; incontinence pads; feminine hygiene products; allergen replacement. © Munksgaard, 1996.

People used to become sensitized to rosin (colophony) from plaster with rosin-containing adhesive. The use of rosin in plasters has decreased in Sweden, but in the Swedish multicentre patch test study from 1991-1993, colophony was still ranked the 5th most common cause of positive patch test reactions (1). We have previously detected rosin components in paper and paper products (2-5). Most patch test reactions were seen to acetone extracts of papers of mechanical pulps from coniferous woods (pine and spruce), since rosin components remain in these pulps (5).

Disposable paper diapers (napkins) have now become the first choice in many countries. In 1992, about 97% of Swedish consumers used diapers based on fluff pulp, almost all disposable and of the "all-in-one" type. A cross-section of such a diaper is shown in Fig. 1. The coverstock in close contact with the skin is a sheet of nonwoven material, most often polypropylene but also polyethylene or polyester. This sheet is glued to the cellulose fluff. Many disposable diapers also contain absorbent gelling material ("superabsorbent"), consisting of cross-linked sodium polyacrylates either blended with the fluff or distributed on the cellulose mat surface. A backsheet of polyethylene covers the outside of the fluff. The fluff consists of mechanical (chemi-thermomechanical, CTM) or chemical pulps, or a combination of both. Threads of latex are used to obtain a better fit of the diapers (6, and personal communication from diaper producers).

According to the literature (7), fluff pulp is an important pulp grade used as the absorbent medium in disposable diapers, feminine hygiene products and hospital pads. Traditionally, long-fibred chemical pulps (kraft or sulfite) have been used, but more recently, less-expensive mechanical grades have taken a significant share of the market.

As part of the investigation of sources of exposure to rosin allergens, some of the most common disposable diapers on the Swedish market were analyzed for rosin components.

6 "all-in-one" diapers common on the Swedish market in 1993 were purchased and analyzed. Diapers from the 2 major producers were also purchased and analyzed in 1995. The nonwoven material from one of the diapers was obtained from the producer before it was glued to the cellulose mat. Abietic acid and dehydroabietic acid were obtained from Helix Biotech, Vancouver, Canada, and purified at our laboratory. 7-oxodehydroabietic acid was prepared in our laboratory (8). Standard chemicals used were of analytical or pharmaceutical grade.

The diapers were divided into 3 parts: the backsheet (including the glue), the fluff, and the top layer (including the coverstock and the glue, together with small amounts of the fluff) (Fig. 1). The tissue sheet found in 1 of the diapers was omitted. The top layer and the cellulose fluff were analyzed chemically to detect rosin compounds. Acetone extracts were prepared from samples of these parts of the diapers in the same way as previously reported for paper extraction (3, 5). About 2.5 g of the top layer and 12.5 g of the fluff were cut into small pieces; 100 ml acetone was added and the mixture stirred in ultrasound for 10 min. The solvent was decanted and extraction with 100 ml acetone repeated. The 2 extracts were pooled and concentrated to dryness. The concentrates were stored under nitrogen.

Fig. 1. A cross-section of the middle part of an "all-in-one" diaper. 1. coverstock of nonwoven material, 2. glue, 3. pulp and superabsorbent polymer, 4. tissue layer in one of the diapers investigated, 5. backsheet. The parts of the diapers that were analyzed in the study are shown.

Table 1. Rosin components detected in 6 different "all-in-one" diapers according to GC analyses

Gas chromatographic (GC) analyses were performed to detect the main rosin compounds, abietic acid and dehydroabietic acid, and also the oxidation product, 7oxodehydroabietic acid, in the diaper extracts. Prior to analysis, the extracts were methylated with diazomethane. (Caution! Diazomethane is highly explosive and carcinogenic.) The solvent used in the analyses was dichloromethane. The injection concentration was 1000 ng/µl for the extracts of the diaper material and 15 ng/µl for the references. The analyses were performed with on-column injection technique on a fused silica column (HP-1, stationary phase 0.52 µm, length 25 m, i.d. 0.31 mm) using an FI detector. The column temperature of 35°C at injection was raised to 210°C (20°C/min) and further to 240°C (5°C/min). The detector temperature was 250°C. Nitrogen was used as carrier gas (1.96 ml/min).

Methylated pure compounds were used as references and methyl stearate as internal standard. The retention time relative to the internal standard was calculated for each compound. Only peaks that gave the correct value compared to reference substances were accepted. Reference compounds were co-injected with the extracts of some of the diapers to confirm the presence of the compounds in the material. Each analysis was performed 2 X .

The results of the analyses of the content of rosin components in the different diapers are shown in Table 1. Rosin components (mainly abietic acid and dehydroabietic acid) were detected in all diapers. No rosin components were detected in the coverstock of diaper F₉₅ before it was glued to the cellulose mat. A gas chromatogram from the analysis of the fluff of diaper F₉₅ is shown (Fig. 2).

Diaper (napkin) dermatitis is one of the most common dermatoses in infants. Diapering promotes adverse changes in the skin through increases in hydration and pH. This makes the skin more susceptible to mechanical chafing, chemical and enzymatic irritants, and microbial attack. A statistical association between diaper dermatitis and elevated skin wetness and pH has been described (9). Disposable diapers containing gelling material give less diaper dermatitis than conventional disposable and cloth diapers, due to improved dryness (10).

Fig. 2. Gas chromatographic analysis of the rosin components in fluff of diaper F₉₅. Peak A: internal standard (methyl stearate); peak B: dehydroabietic acid; peak C: abietic acid. The material was methylated with diazomethane before analysis.

According to Longhi et al. (11), endogenous factors, such as atopy and age, and exogenous factors, such as diseases and the drugs used to treat them, strongly influence the incidence of diaper dermatitis. The question raised in the study is whether rosin allergens present in disposable diapers could cause allergic contact dermatitis in some cases.

Rosin components were detected in all the diapers that we analyzed in 1993. The most rosin was detected in those from the 2 major producers (E and F, Table 1). Diapers from these producers available on the market in 1995 still contained rosin, according to chemical analyses. In some diapers (A, E, F, Table 1), more rosin was detected in the top layer, which is in close contact with the skin, than in the fluff, although the coverstock consists of non-woven material commonly made from polypropylene. However, the coverstock is glued to the cellulose mat, and the glue was included in the top layers taken from the diapers for analysis, since it could not be removed. Analysis of the coverstock from diaper F₉₅, before it was glued to the cellulose mat, revealed no rosin components. According to the producer of the F diapers, no rosin should be present in the glue used for these diapers. However, neither the composition of the glue nor a sample for analysis were obtained from the producer. Modified rosin is commonly used in glues. According to a Swedish report (12), the glues used in diapers are commonly based on ethylvinylacetate and contain resins, softening agents and antioxidants. If the glue in question is stated to contain modified rosin, the content of unmodified residual material would not be declared. That unmodified rosin is still present in modified rosin products is not generally known (13, 14).

It is not possible to analyze for all compounds of rosin, due to its complex chemical composition, which also varies depending on source, method of recovery, storage and handling. We chose abietic acid and dehydroabietic acid as screening substances for the presence of rosin in various products, since these are the major compounds in most unmodified rosins, which usually contain 30-50% of abietic acid. Although we have found these acids to be non-allergenic in themselves, their presence indicates the presence of allergenic oxiation products (15-19). 1 such product, 7-oxodehydroabietic acid (20), was also used for determinating rosin content, since it is stable and easily analyzed. However, we could not identify this compound in most of the diaper material analyzed, since peaks from other components interfered: these could be other oxidation products.

Since there are no studies demonstrating the lowest concentration of rosin to sensitize in humans, we cannot say whether the amounts detected in diapers are sufficient to cause sensitization.. Penetration of such compounds in the diaper area would be enhanced by close skin contact, occlusion and irritation, which increases the risk of sensitization (21). Allergic contact dermatitis is less common in children under 3-4 years than in older children (22). The most frequently recognized causes of such contact sensitivity are nickel, balsam of Peru and rubber chemicals (21). However, patch testing in children with eczema is restricted, since they are not supposed to be exposed to contact allergens in the first years of life. This restriction also minimizes the risk of sensitization by patch testing (23).

In previous studies in patients with contact allergy to rosin and hand eczema, their eczema healed if they wore cotton gloves when handling paper (3, 24). The content of rosin components in paper based on mechanical pulp from coniferous woods is in the range of 50-300 ppm (3, 5). Thus, the amount of rosin components detected (20-200 ppm) in 6/8 analyzed diapers might be expected to elicit dermatitis in previously sensitized persons. Furthermore, the chief way of bleaching mechanical, e.g., CTM pulp used in diapers is with hydrogen peroxide under alkaline conditions. This improves brightness without significant yield loss (25). Resin acids incorporated in the pulp are actively oxidized by this bleaching technique (26), thus possibly increasing the potential of the material to cause allergic contact reactions. The major producers of the diapers in this study have been informed of the results and are aware of the problems.

We have here exemplified 1 of the many sources of rosin exposure in our surroundings. Although the risk of sensitization to rosin allergens in diapers might be considered minimal, it is important to be aware of the risk of elicitation in sensitive individuals, especially since penetration is enhanced by occlusion and irritation. Such material is used not only for infant diapers but also for adult incontinence products and feminine hygiene products. The glue used in some diapers seems to be a source of rosin allergens and should be exchanged for a rosin-free alternative. Minimal amounts of rosin allergens are unavoidable in paper products based on pulp from coniferous woods. The content depends on the method of production. In chemical pulp, a major part of the rosin is separated and refined, to give tall oil rosin as a by-product while for mechanical pulp, the rosin components remain incorporated. The growing importance of mechanical pulps for production of fluff thus increases the risk of allergic contact dermatitis.

We thank Dr. Elisabeth Gäfvert for valuable discussions. This work was supported by a grant from The Swedish Asthma and Allergy Association.

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Address:
Ann-Therese Karlberg
Division of Occupational Dermatology
National Institute o/ Occupational Health
S-171 84 Solna
Sweden