Elicitation Threshold Research Articles

Skin sensitisation elicitation: Evaluation of the general threshold and considerations for use.

Allergic contact dermatitis (ACD) is an immune response to chemical haptens, involving induction and elicitation phases. Quantitative risk assessment (QRA) reviewing the skin sensitisation potential for all ingredients and using chemical-specific induction thresholds for skin allergens remains the current best approach for the safety evaluation of consumer products. However, elicitation thresholds have utility in secondary protection for pre-sensitised consumers. The objectives were to (1) review the current elicitation threshold database, (2) evaluate whether predicted relationships between chemical induction and elicitation potencies enable elicitation threshold prediction and (3) discuss elicitation threshold utility as a secondary method of consumer protection. In total, 28 publications (with 39 elicitation datasets) were included in non-linear regression analysis to derive elicitation thresholds for 22 allergens, including fragrances, preservatives and metals. The median elicitation threshold (ED10) for the expanded database was 0.95 μg/cm2, which supports previously published general elicitation thresholds. The derived ED10 for each chemical had only weak to moderate correlation with corresponding induction thresholds, thus limiting suitability as the predictive model. Assessment of current EU fragrance allergen labelling and sensitiser labelling under the globally harmonised system in the context of general and chemical-specific elicitation thresholds shows that current practices are health protective.

Analysis of Contact Allergens in Polyvinyl Chloride Examination Gloves in the United States.

Background: Polyvinyl chloride (PVC) gloves are recommended as a safe alternative for patients with rubber accelerator allergy. However, allergic contact dermatitis to other chemicals in PVC gloves has been reported. Objective: To analyze single-use PVC medical examination gloves in the United States for the presence of potential contact allergens. Methods: Using liquid chromatography-mass spectrometry, 20 unique PVC gloves were analyzed in triplicate for 6 chemicals: benzisothiazolinone, bisphenol A, mono(2-ethylhexyl) maleate, tricresyl phosphate, triphenyl phosphate, and triphenyl phosphite. Results: All 20 PVC gloves contained detectable quantities of benzisothiazolinone (range, 0.001-1.48 parts per million [ppm]), bisphenol A (0.01-0.11 ppm), triphenyl phosphate (0.01-2.11 ppm), and triphenyl phosphite (0.001-0.22 ppm). Eighteen (90%) gloves contained mono(2-ethylhexyl) maleate (0.001-0.14 ppm) and 3 (15%) contained tricresyl phosphate (0.001-0.002 ppm). Conclusions: Known allergens were present in all 20 PVC gloves. However, the detected levels were mostly low and their relationship with sensitization and elicitation thresholds requires further study.

Patch test-relevant concentrations of metal salts cause localized cytotoxicity, including apoptosis, in skin ex vivo.

BackgroundMetal alloys containing contact sensitizers (nickel, palladium, titanium) are extensively used in medical devices, in particular dentistry and orthopaedic surgery. The skin patch test is used to test for metal allergy.ObjectiveTo determine whether metal salts, when applied to freshly excised skin at patch test–relevant concentrations and using a method which mimics skin patch testing, cause in changes in the epidermis and dermis.MethodsTissue histology, apoptosis, metabolic activity, and inflammatory cytokine release were determined for two nickel salts, two palladium salts, and four titanium salts.ResultsPatch test–relevant concentrations of all metal salts caused localized cytotoxicity. This was observed as epidermis separation at the basement membrane zone, formation of vacuoles, apoptotic nuclei, decreased metabolic activity, and (pro)inflammatory cytokine release. Nickel(II) sulfate hexahydrate, nickel(II) chloride hexahydrate, titanium(IV) bis(ammonium lactato)dihydroxide, and calcium titanate were highly cytotoxic. Palladium(II) chloride, sodium tetrachloropalladate(II), titanium(IV) isopropoxide, and titanium(IV) dioxide showed mild cytotoxicity.ConclusionThe patch test in itself may be damaging to the skin of the patient being tested. These results need further verification with biopsies obtained during clinical patch testing. The future challenge is to remain above the elicitation threshold at noncytotoxic metal concentrations.

Microglia alter the threshold of spreading depolarization and related potassium uptake in the mouse brain

Selective elimination of microglia from the brain was shown to dysregulate neuronal Ca2+ signaling and to reduce the incidence of spreading depolarization (SD) during cerebral ischemia. However, the mechanisms through which microglia interfere with SD remained unexplored. Here, we identify microglia as essential modulators of the induction and evolution of SD in the physiologically intact brain in vivo. Confocal- and super-resolution microscopy revealed that a series of SDs induced rapid morphological changes in microglia, facilitated microglial process recruitment to neurons and increased the density of P2Y12 receptors (P2Y12R) on recruited microglial processes. In line with this, depolarization and hyperpolarization during SD were microglia- and P2Y12R-dependent. An absence of microglia was associated with altered potassium uptake after SD and increased the number of c-fos-positive neurons, independently of P2Y12R. Thus, the presence of microglia is likely to be essential to maintain the electrical elicitation threshold and to support the full evolution of SD, conceivably by interfering with the extracellular potassium homeostasis of the brain through sustaining [K+]e re-uptake mechanisms.

Allergic contact dermatitis caused by hydroperoxides of limonene and dose-response relationship-A repeated open application test (ROAT) study.

Contact allergy to oxidized limonene, with hydroperoxides of limonene (Lim-OOHs) as the main allergens, is common. However, high proportions of weak positive and doubtful patch test reactions have been reported. To determine the clinical relevance, elicitation threshold and dose-response relationship of Lim-OOHs in individuals with a positive or doubtful patch test reaction to standard Lim-OOHs 0.3% pet. A multicentre 3-week double-blind vehicle-controlled repeated open application test (ROAT) study with a simulated fine fragrance containing Lim-OOHs at 1260, 420 and 140 ppm, equal to a dose/area per application of Lim-OOHs of 3.0, 0.99 and 0.33 μg/cm2 , was performed. Among 11 subjects allergic to Lim-OOHs, 11 (100%), 7 (64%), and 3 (27%), respectively, reacted to the applied doses. No reactions were seen in 17 healthy controls exposed to the highest dose. This difference in reactivity was statistically significant (P < 0.0001). Among 13 subjects with doubtful patch test reactions to Lim-OOHs, two (15%) had positive ROAT reactions to the highest Lim-OOH dose applied (P = 0.36 as compared with controls). Contact allergy to Lim-OOHs is of clinical relevance in patients with positive patch test reactions. A doubtful patch test reaction to Lim-OOHs 0.3% pet. can be of clinical relevance.

Rational ideation and empiric validation of an innovative digital dermographic tester.

Dermographism is a condition characterized by a weal response to a combination of pressure and traction on skin surface, and its diagnosis is based on medical history, clinical criteria and provocation test. The Dermographic Tester® , a pen-sized tool containing a spring-loaded blunt tip, is the most widely used instrument for the provocation test, and it exerts increasing pressures on the skin surface according to an arbitrary units (AU) scale. Analysing the mechanism of function and trying to convert the AUs to SI units (g/mm2 ), we found that this instrument had some defects and limits that would compromise a true and repeatable quantification of the weal response threshold. Consequently, we decided to develop a new instrument, the Digital Dermographic Tester (DDT), which is engineered with an inside force sensor to implement features lacking in the current tools, in the hope of enhancing the precision of the provocation test. To validate the effectiveness and accuracy of the DDT. We tested the DDT on 213 participants purposely sampled to obtain three groups, each with a different pattern of reaction to mechanical stimuli. Based on anamnestic, diagnostic and symptomatic criteria, patients were divided into dermographic urticaria (DU), spontaneous urticaria (SU) and healthy control (HC) groups. The DDT was used to apply 12 levels of pressure to the skin surface, and a frequency distribution of positive reactions was displayed for each group. A force of 36-40 g/mm2 appropriately differentiated physiological from pathological conditions with high sensitivity and specificity. The DDT was found to be capable of differentiating patients with DU patients from those with SU and from HCs, and was able to precisely identify the weal elicitation threshold.

Elicitation threshold of cobalt chloride: analysis of patch test dose-response studies.

Cobalt is a strong skin sensitizer (grade 5 of 5 in the guinea-pig maximization test) that is used in various industrial and consumer applications. To prevent sensitization to cobalt and elicitation of allergic cobalt dermatitis, information about the elicitation threshold level of cobalt is important. To identify the dermatitis elicitation threshold levels in cobalt-allergic individuals. Published patch test dose-response studies were reviewed to determine the elicitation dose (ED) levels in dermatitis patients with a previous positive patch test reaction to cobalt. A logistic dose-response model was applied to data collected from the published literature to estimate ED values. The 95% confidence interval (CI) for the ratio of mean doses that can elicit a reaction in 10% (ED(10)) of a population was calculated with Fieller's method. On the basis of five included studies, the ED10 values of aqueous cobalt chloride ranged between 0.0663 and 1.95 µg cobalt/cm(2), corresponding to 30.8-259 ppm. Our analysis provides an overview of the doses of cobalt that are required to elicit allergic cobalt contactdermatitis in sensitized individuals, and thereby the basis for future prevention of cobalt allergy.

Analysis of the interrelationship of the pulmonary irritation and elicitation thresholds in rats sensitized with 1,6-hexamethylene diisocyanate (HDI)

This paper summarizes a range of experimental data central for developing a science-based approach for hazard identification of monomeric and polymeric aliphatic 1,6-hexamethylene diisocyanate (HDI). The dose–response curve of HDI-induced pulmonary responses in naïve or dermally sensitized rats after one or several inhalation priming exposures was examined in the Brown Norway (BN) rat asthma model. Emphasis was directed to demonstrate the need and the difficulty in selecting an appropriate pulmonary dose when much of the inhaled chemically reactive vapor may concentration dependently be retained in the upper airways of obligate nose-breathing rats. The course taken acknowledges the experimental challenges in identifying an elicitation threshold for HDI-monomer near or above the saturated vapor concentration or in the presence of a HDI-polymer aerosol. The inhalation threshold dose on elicitation was determined based on a fixed concentration (C) × variable exposure duration (t) protocol for improving inhalation dosimetry of the lower airways. Neutrophilic granulocytes (PMN) in bronchoalveolar lavage (BAL) fluid in equally inhalation primed naïve and dermally sensitized rats were used to define the inhalation elicitation threshold C × t. Sensitized rats elaborated markedly increased PMN challenged sensitized rats relative to equally challenged naïve rats at 5625 mg HDI/m3 × min (75 mg/m3 for 75 min). PMN were essentially indistinguishable at 900 mg HDI/m3 × min. By applying adjustment factors accounting for both inter-species differences in inhalation dosimetry and intra-species susceptibility, the workplace human-equivalent threshold C × t was estimated to be in the range of the current ACGIH TLV® of HDI. Thus, this rat “asthma” model was suitable to demonstrate elicitation thresholds for HDI-vapor after one or several inhalation priming exposures and seems to be suitable to derive occupational exposure values (OELs) for diisocyanates in general.

The nickel dose–response relationship by filaggrin genotype (FLG)

On skin contact, nickel accumulates in the stratum corneum, where it is probably bound to proteins and amino acids. One probable contributor is filaggrin, which binds nickel avidly. Filaggrin gene (FLG) null mutations lead to a complete lack of filaggrin production from the affected allele, and have been associated with an increased risk of nickel contact sensitization in German and Danish adults. To investigate whether the experimental nickel elicitation threshold level differed between heterozygous FLG mutation and non-mutation carriers. Thirteen nickel-sensitized female patients, seven heterozygous mutation carriers and six non-mutation carriers (genotyped for R501X, 2282del4, or R2447X), were patch tested and performed a repeated open application test (ROAT) with a nickel sulfate dilution series. Logistic threshold dose-response analyses were used to test for differences between the two groups. No difference was found in the dose-response relationship between FLG mutation and non-mutation carriers. On the basis of this small patient study, it appears that the elicitation threshold level for nickel is independent of FLG null mutation single-allele carrier status.

Formaldehyde in textiles–what dermatologists need to know about the relationship to contact dermatitis: A review of the US Government Accountability Office's Report to Congressional Committees

does not contain recommendations. 1 However, pertinent information can be gleaned for dermatologists caring for patients with contact dermatitis that may be related to formaldehyde resins found in many types of textiles. The GAO report tested 180 items for formaldehyde release, using two different tests that have been developed and used by the textile industry. The most frequently used is the Japanese Industrial Standard L 1041 Test, which was developed to measure the amount of formaldehyde that may be released by clothing and other textiles that come into contact with the skin. The American Association of Textile Chemists and Colorists 112 Test, which was developed to measure the amount of formaldehyde that may be released from clothing and other textiles during extended storage or hot and humid conditions, 2 is also used in 5 of the 14 studies analyzed in the GAO report. The United States does not have regulations on detectable limits for textiles made in this country, but the majority of items tested would have met the American Apparel and Footwear Association’s most stringent regulations in other countries. 3 Of the 180 items tested, 10 exceeded the acceptable limits defined as less than 75 ppm for products that come into direct contact with the skin, as minimum elicitation thresholds may be as low as 30 ppm in some individuals. Of these, half indicated ‘‘easy care’’ characteristics such as: wrinkle free, stain resistant, and no iron. As expected, all were either 100% cotton or a cotton/polyester or cotton/nylon blend. The most problematic items were adult pillowcases (3/12 released excessive formaldehyde), and men’s and boy’s dress shirts (3/15). Additional itemstestingpositiveincludedapairofmen’skhakis, a child’s hat, a crib sheet, and a pair of US military combat pants. A total of 25 additional items released formaldehyde at a level that was below the lowest acceptable limit, and 145 items released no detectable formaldehyde.

A quantitative approach to assess the potency of skin sensitizers in the elicitation phase

The concept that thresholds exist for the induction of allergic contact dermatitis by chemicals with skin sensitizing properties has been used for a quantitative risk assessment approach. In this approach the potency of skin sensitizers as determined in the Local Lymph Node Assay is used to calculate the threshold for induction of sensitization. These are then used to estimate safe exposure levels for consumers. Whether these exposure levels will protect subjects that are already sensitized is unknown. The elicitation of allergic contact dermatitis supposedly occurs above a certain threshold as well and this threshold is most likely lower than that for the induction. It is unclear if induction thresholds can be extrapolated to elicitation thresholds. The aim of this study was to assess the potency of sensitizers with different sensitizing potencies in the elicitation phase in a mouse model for elicitation. Mice were sensitized by topical application on days 0 and 7 using equipotent concentrations of oxazolone, 2,4-dinitrochlorobenzene (DNCB) and eugenol to ensure that the sensitization strength would not influence the elicitation potency. Mice were challenged on day 21 by topical application on the ears in a dose-dependent manner and dose–response data were used to calculate the elicitation potency. Unexpectedly, sensitizers with different sensitizing potencies induced not the same dose–response curves in sensitized mice. The most potent sensitizer in the elicitation phase was oxazolone, followed by DNCB and eugenol. Similar to the induction phase, under equipotent sensitization conditions strong sensitizers such as oxazolone and DNCB elicit allergic reactions at lower concentrations than weak sensitizers such as eugenol. Our results indicate that elicitation thresholds cannot be readily deduced from sensitization thresholds.

A pilot study aimed at finding a suitable eugenol concentration for a leave‐on product for use in a repeated open application test

Knowledge of sensitization and elicitation thresholds and the time-dose relationship for elicitation of contact dermatitis is important in order to provide safe products for consumers. Since previous studies performed with eugenol had showed negative results in a repeat open application study (ROAT) study, we wanted to perform a ROAT with higher concentration (maximum allowed) and longer ROAT. 5 volunteers previously tested positive to eugenol were studied. They performed a ROAT test for maximum 4 weeks with four different solutions. Results. Four of five reacted to the maximum concentration of eugenol in the ROAT. In patients sensitized to eugenol, with the maximum allowed concentration of eugenol and given a prolonged ROAT (4 weeks), there is a clear risk of elicitating an allergic contact dermatitis.

Report on Stakeholders' activities in the area of emerging risks

Report on Stakeholders' activities in the area of emerging risks

Can exposure limitations for well-known contact allergens be simplified? An analysis of dose-response patch test data

Allergic contact dermatitis is triggered by chemicals in the environment. Primary prevention is aimed at minimizing the risk of induction, whereas secondary and tertiary prevention are aimed at reducing elicitation. To identify the elicitation doses that will elicit an allergic reaction in 10% of allergic individuals under patch test conditions (ED(10) patch test) for different allergens, and to compare the results with those for different allergens and with animal data indicating sensitizing potency from the literature. The literature was searched for patch test elicitation studies that fulfilled six selected criteria. The elicitation doses were calculated, and fitted dose-response curves were drawn. Sixteen studies with eight different allergens-methylchloroisothiazolinone/ methylisothiazolinone, formaldehyde, nickel, cobalt, chromium, isoeugenol, hydroxyiso hexyl 3-cyclohexene carboxaldehyde, and methyldibromo glutaronitrile-were selected. The median ED(10) value was 0.835 µg/cm(2). The ED(10) patch test values were all within a factor of 7 from the lowest to the highest value, leaving out three outliers. No obvious patterns between the sensitization and elicitation doses for the allergens were found. We found a rather small variation in the ED(10) patch test between the allergens, and no clear relationship between induction potency and elicitation threshold of a range of allergens. This knowledge may stimulate thoughts on introducing a generic approach for limitations in exposure to well-known allergens.

Sacral neurophysiologic study in patients with chronic spinal cord injury

Neurophysiologic testing of the sacral reflex has demonstrated utility in the diagnosis of sacral lower motor neuron lesions. The aim of the present study was to also apply this test to patients with upper motor neuron lesions. A group of 16 male patients with chronic suprasacral spinal cord lesions was prospectively recruited. In addition to history and clinical neurologic examination (including anal sphincter tone, saddle sensation, and penilo-cavernosus reflex testing), sacral neurophysiologic studies were performed. Neurophysiologic testing included quantitative electromyography of the external anal sphincter (motor unit potential (MUP) count during relaxation and MUP analysis), and neurophysiologic measurement of the penilo-cavernosus reflex (elicitation threshold and latency) on electrical stimulation. The findings were compared to data obtained in the control group of 26 men. Clinical elicitability of the penilo-cavernosus reflex was increased, and the neurophysiologically measured reflex threshold reduced in patients (<0.02). No significant differences were found in clinical assessment of anal sphincter tone, MUP count, reflex latency, and quantitative MUP analysis. The diagnostic sensitivity of individual parameters was low (≤25%). In patients with chronic spinal cord injury, increased elicitability of the penilo-cavernosus reflex was found. However, none of the assessed neurophysiologic parameters was found to assist in the diagnosis of the sacral upper motor neuron lesion in individual patients. The shortened sacral reflex latency found in individual patients is therefore not a consequence of a suprasegmental lesion, but rather of the low position of the conus medullaris (e.g., in tethered cord syndrome).

Brown Norway rat asthma model of diphenylmethane-4,4′-diisocyanate (MDI): Determination of the elicitation threshold concentration of after inhalation sensitization

Occupational exposure to polymeric diphenylmethane-diisocyanate (MDI), a known human asthmagen, can be attributed to two potential routes: the skin and the respiratory tract. While the skin as the route of sensitization was the focus of a previous investigation (Pauluhn, 2008), this paper describes a modified sensitization protocol using a 5-day inhalation exposure (days 0–4) of Brown Norway (BN) rats to two concentration × exposure time ( C × t) relationships of 1000, 5000, and 10,000 mg MDI/m 3 × min at exposure durations of either 10 or 360-min. Apart from the differences in the induction protocol, all other experimental variables remained identical. This was followed by four 30-min inhalation challenges to 40 mg MDI/m 3 on target days 20, 25, 50, and 65. After the last challenge, changes in breathing patterns delayed in onset were recorded and allergic lung inflammation was probed by bronchoalveolar lavage (BAL). In a subsequent study groups of rats were sensitized using the 10-min C × t protocol and challenged 3-times at 40 mg MDI/m 3. At the fourth challenge a dose-escalation regimen was used to determine the elicitation threshold on ‘asthmatic’ rats. Consistent with the skin-sensitization protocol, the most sensitive endpoints characterizing an allergic pulmonary inflammation were again BAL-neutrophils and physiological measurements showing respiratory changes delayed in onset. The dose-escalation challenge yielded an elicitation threshold of 5 mg MDI-aerosol/m 3 at 30 min challenge duration. In topically sensitized rats this threshold was estimated to be 3 mg/m 3. In summary, these data suggest the C × t product of MDI-aerosol that triggers an elicitation response in ‘asthmatic’ rats is slightly below of that causing acute pulmonary irritation in naïve rats. The high concentration delivered to the respiratory tract during the 10-min exposure period elicited a more vigorous response than the similar C × t at 360 min. Therefore, short high-level exposure patterns appear to bear a higher sensitizing potency than equal C × t products at longer exposure periods. Taking into account the respective differences in exposure intensities, the comparison of elicitation thresholds of BN rats sensitized by inhalation or skin exposure did not demonstrate essential differences.

Susceptibility and reactivity in polysensitized individuals following controlled induction

It is uncertain whether polysensitized patients acquire multiple allergies only because of a high degree of exposure to environmental allergens, or because of being highly susceptible to developing contact allergy. The aim of this study was to investigate and compare susceptibility and reactivity in polysensitized and monosensitized individuals, and in healthy controls. We sensitized 66 adult individuals (21 polysensitized, 22 monosensitized, and 23 healthy controls) with diphenylcyclopropenone and assessed challenge responses with visual scoring and ultrasound. We compared sensitization rates using a chi-square test and logistic regression analyses, and calculated linear regression lines of the elicitation responses for each individual. The mean values of the slopes and the intercepts for each group were used to measure the strength of the elicitation response, and were compared using the Mann-Whitney test. Sensitization ratio was equal in the three groups: 57% for the polysensitized, 59% for the monosensitized, and 65% for the healthy control group. There was a lowered elicitation threshold in the polysensitized group compared with that in the monosensitized and healthy control groups and, although not statistically significant, a stronger elicitation response was observed in the polysensitized group. Increased reactivity was found in the polysensitized group, demonstrated by a lowered elicitation threshold, compared with that in the monosensitized and healthy control groups.

Does allergic contact dermatitis from formaldehyde in clothes treated with durable‐press chemical finishes exist in the USA?

Recent US studies have presented case series of patient with allergic contact dermatitis (ACD) allegedly caused by formaldehyde in clothes treated with durable-press chemical finishes (DPCF), which are known formaldehyde releasers. However, the amounts of formaldehyde released by modern DPCF are thought to be well below the levels previously estimated to be able to elicit ACD. The objectives of this review are (i) to investigate whether clothes sold in the USA may contain enough free formaldehyde to elicit ACD in previously sensitized individuals and (ii) to assess the validity of US reports on ACD from formaldehyde in DPCF treated clothes. Literature was examined using various resources. The threshold level for formaldehyde in clothes that may cause ACD in sensitized individuals is unknown; we present data suggesting that levels < 200 ppm will be safe for most patients and that textiles will rarely contain higher amounts. All US studies presenting patients with ACD from formaldehyde in clothes had some weaknesses and in no report was the diagnosis proven beyond doubt. Currently, there is no definite proof that textile ACD from formaldehyde in DPCF in the USA exists. Future research should be directed at establishing the elicitation threshold and the amounts of formaldehyde present in textiles.

The Key Events Dose-Response Framework: A Foundation for Examining Variability in Elicitation Thresholds for Food Allergens

Food allergies are caused by immunological reactions in individuals sensitized to normal protein components of foods. For any given sensitized individual, the severity of a reaction is generally assumed to be proportional to the dose of allergenic protein. There is substantial clinical evidence that “threshold” doses exist for the elicitation of an allergic reaction; however, the threshold (i.e., lowest dose that elicits a reaction) varies substantially across the sensitized population. Current approaches to protecting sensitized individuals from exposure to food allergens are highly qualitative (i.e., they rely on food avoidance). The Key Events Dose-Response Framework is an analytical approach for refining understanding of the biological basis of the dose-response. Application of this approach to food allergy provides a foundation for a more rigorous quantitative understanding of variability in allergic response. This study reviews the allergic disease process and the current approaches to identifying thresholds for food allergens. The pathway of key biological events occurring between food intake and allergic response is considered, along with factors that may determine the nature and severity of response to food allergens. Data needs, as well as implications for identifying thresholds, and for characterizing variability in thresholds, are also discussed.

Hydroxyisohexyl 3-cyclohexene carboxaldehyde allergy: relationship between patch test and repeated open application test thresholds

Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) is a synthetic fragrance ingredient. Case reports of allergy to HICC appeared in the 1980s, and HICC has recently been included in the European baseline series. Human elicitation dose-response studies performed with different allergens have shown a significant relationship between the patch-test threshold and the repeated open application test (ROAT) threshold, which mimics some real-life exposure situations. Fragrance ingredients are special as significant amounts of allergen may evaporate from the skin. The study aimed to investigate the relationship between elicitation threshold doses at the patch test and the ROAT, using HICC as the allergen. The expected evaporation rate was calculated. Seventeen HICC-allergic persons were tested with a dilution series of HICC in a patch test and a ROAT (duration up to 21 days). Seventeen persons with no HICC allergy were included as control group for the ROAT. Results The response frequency to the ROAT (in microg HICC cm(-2) per application) was significantly higher than the response frequency to the patch test at one of the tested doses. Furthermore the response rate to the accumulated ROAT dose was significantly lower at half of the doses compared with the patch test. The evaporation rate of HICC was calculated to be 72% over a 24-h period. The ROAT threshold in dose per area per application is lower than the patch test threshold; furthermore the accumulated ROAT threshold is higher than the patch test threshold, which can probably be explained by the evaporation of HICC from the skin in the open test.