Testing with the Patient’s Own Products

Pro’s

Practical: products at hand and actually contacted by the patient

Own products: contain other allergens not present in series or commercialized (always incomplete and not updated)

Have physicochemical properties that might be different from the commercial patch test allergens

May contain allergenic impurities or additives

Picks up “compound allergy” (to a product in which the allergen might penetrate better into the skin or in which a new allergen has been formed; indeed, chemical ingredients may interact)

Possibly identifies new allergens

Confirms the relevance of a positive test

Contra’s

No “standardized” testing

Requires knowledge of the materials to be tested

Requires a lot of expertise from the examiner

May produce both false-positive and false-negative test results

4.2 Methodology

Guidelines for testing with the patients’ own materials have already been extensively described [1]; the materials most frequently tested are usually topical medications, cosmetics of various types, and rubber and leather products. It is very important though that information on the test material is obtained before skin testing. While the complete composition of pharmaceutical and cosmetic products is known, with regard to industrial products (e.g., metalworking fluids, glues, paints, etc.), the material safety data sheets provide only basic information and do not list all allergy-relevant ingredients. In addition, the producer selling the product is often not aware of contaminants or materials under a different nomenclature.

When a positive test occurs with the patient’s own product, further testing with the ingredient is essential.

When a cosmetic product is involved, manufacturers may provide the ingredients at adequate dilutions and vehicles for patch testing; however, some tend to supply the ingredients in dilutions as used in the products, producing false-negative reactions on patch testing. Furthermore, coded material obtained from a manufacturer without knowing the details on the chemical regarding toxicity and appropriate test concentration should never be applied.

The possible methodologies involved in testing with the patient’s own products are shown in Table 4.2. Besides patch testing and photopatch testing in case photoallergic contact dermatitis is suspected [2], open and “semi-open or semiocclusive tests” [3] or use tests [4] and repeated open application tests (ROATs) [5] are useful additional methods to identify the culprits.

Table 4.2

Test methodology

Patch tests

Photopatch tests

(Semi-)open or semiocclusive tests

ROATs (repeated open application tests)

Use tests (at original site)

Prick testing (in case of immediate skin reactions or protein contact dermatitis)

4.2.1 Patch Tests and Semi-Open Tests

Patch tests are performed with products that do not contain irritant ingredients such as cosmetic and pharmaceutical creams, lotions, etc., while open and semi-open (or semiocclusive) tests are particularly helpful if irritant reactions under occlusion are to be suspected, e.g., in the case of cosmetics such as shampoos, liquid soaps, and nail varnish; medicaments containing irritating constituents, such as benzoyl peroxide, tretinoin, capsaicin, PVP-iodine, or quaternary ammonium compounds; and industrial products such as glues, paints, inks, varnishes, etc. The material is applied to the skin with a cotton swab (about 15 μl) on a small area (2 × 2 cm), left for drying (possibly dabbing with another Q-tip or tissue) and then covered with acrylic tape (only when completely dried). Sometimes a weak irritant response to a product tested as such semi-open may be observed, but then this method can also be used for diluted products (e.g., shampoos, soaps, paints, etc.).

The golden rule is that when a subject comes directly in skin contact with a product that has irritant properties (either on purpose, e.g., cleansing products, or accidentally, e.g., soluble oils, paints), then the product may be tested in this way.

However, corrosive or other toxic materials (pH <3 or >10) that are normally used in closed systems only or with protection by appropriate clothing are excluded from testing. At pH of 4–9, very few irritant reactions are caused by the acidity or alkalinity itself, and buffering solutions may be used ([6], Table 4.3).

Table 4.3

Composition of buffer solution, pH 4.7, and alkaline buffer solution, pH 9.9 [6]

Compound	Concentration	% of total volume
Acid buffer, pH 4.7
Sodium acetate	0.1 N (8.2 g CH₃COONa/L aqua)	50
Acetic acid	0.1 N (6.0 g CH₃COOH/L aqua)	50
Alkaline buffer, pH 9.9
Sodium carbonate	0.1 M (10.6 g Na₂CO₃/L aqua)	50
Sodium bicarbonate	0.1 M (8.4 g NaHCO₃/L aqua)	50

Solid materials can be tested as such placing scrapings or cut pieces in the test chamber or applied on acrylic tape thus avoiding pressure effects. A piece of the suspected material – textiles, gloves, and shoes – (2 × 2 cm moistened with saline solution), as well as scrapings of (hard) plastic materials, is applied under occlusion for 48 h. However, the reactions may often turn out to be false-negative because the concentration of the sensitizer is too low or the sensitizer is not released. Alternatively, pressure or friction effects of sharp particles may cause some sort of irritant reaction, which should, however, be clearly identifiable as such. Depending on the material, the sensitizer can be extracted with water or solvents ([7], Table 4.4).

Table 4.4

Materials suitable for extraction and recommended solvents [7]

Material	Solvent
Paper	Ethanol
Plants and wood dusts	Acetone, ether, ethanol, or water
Plastics, e.g., gloves	Acetone
Rubber, e.g., gloves	Acetone or water
Textiles	Ethanol

Patch testing with pieces of plants is not recommended in general because irritant reactions are frequent and active sensitization may occur, although direct application on acrylic tape and not occluded by a chamber is less apt to do so. Extracts of plants may be used as well (e.g., [8]). Fine wood dust moistened with physiological saline can be patch tested with a Finn chamber or on adhesive acrylic tape. However, exotic woods can be strongly irritating and sensitizing (teak, rosewood, Macoré) – these should be diluted and tested on acrylic tape (without occlusion) since sensitization might occur even at very low concentrations.

As an additional method, patch testing with thin-layer chromatograms of textiles, gloves, rubber, or any other materials can serve as an elegant adjunct to quickly identify contact allergy to a certain ingredient of a mixture, although the (variable, possibly high) detection limit may yield false-negative results [9].

4.2.2 Use Tests

Use tests at the original site and repeated open application tests (ROATs) are useful additional tests as well. Indeed, patch tests are vastly different from normal use conditions; therefore, tests can be completed by provocative use testing of sensitized subjects. With ROATs, about 0.1 ml of test material is applied twice daily to the flexor aspect of the forearm near the cubital fossa, to an area approximately 5 × 5 cm. The results are read after 1 week, but sometimes ROATs need to be performed up to 21 days, especially with low-concentrated allergens, in order to reveal an allergic reaction.

4.3 Testing for Immediate Reactions to Chemicals and Proteins

As immediate skin reactions are concerned, low molecular chemicals may give rise to contact urticaria (e.g., products containing chlorhexidine, bacitracin, etc.), but also macromolecules can penetrate the skin and are able to induce immunological contact urticaria and/or eczematous clinical pictures, i.e., protein contact dermatitis, most often in an occupational context.

The protein sources are divided into four main groups: group (1) fruits, vegetables, spices, plants, and woods, group (2) animal proteins, group (3) grains, and group (4) enzymes.

To diagnose immediate-type reactions, skin prick tests are the gold standard.

Open testing (quite similar to the skin application food test or SAFT), which has only been mentioned in the diagnosis of food allergy in atopic children, can be helpful but is generally negative unless the substance is applied on damaged or eczematous skin (where it even may cause an immediate vesicular reaction). Sometimes a rubbing test (gentle rubbing with the material) on intact or previously damaged skin might be indicated, if an open test is negative. Scratch and scratch-patch testing carry a higher risk of false-positive reactions, and the latter lacks sensitivity compared to prick testing. Patch tests in protein contact dermatitis are usually negative. If there is a suspicion of any kind of serious extra-cutaneous symptoms, tests should be done with the necessary precautions, and resuscitation facilities should be adequately available [10].