SummaryBackgroundSeveral of the ingredients in fragrance mix I (FM I) have been shown to evaporate from petrolatum preparations applied in test chambers to an extent that can be suspected to affect the patch test result.ObjectivesTo compare the reactivity towards FM I and fragrance mix II (FM II) when they are applied in test chambers in advance and immediately prior to the patch test occasion.MethodsSeven hundred and ninety‐five consecutive patients were simultaneously patch tested with duplicate samples of FM I and FM II. One sample was applied in the test chamber 6 days in advance (6D sample), and the other sample was applied immediately before the patients were patch tested (fresh sample).ResultsTwenty‐two (2.8%) patients reacted exclusively to the fresh sample of FM I, 6 (0.7%) reacted exclusively to the 6D sample, and 22 (2.8%) reacted to both samples. The corresponding numbers for FM II were 9 (1.1%) for the fresh sample, 6 (0.7%) for the 6D sample and 12 (1.5%) for both samples.ConclusionsThere was a statistically significant difference between the numbers of patients reacting to the fresh and 6D samples of FM I. No corresponding difference was observed for FM II. This can probably be explained by differences in volatilities between the ingredients of FM I and FM II.