A volatile fragrance ingredient extracted from geranium, geraniol is capable of causing sensitivity when applied to skin. However, the risk of such reaction has to do with depth of penetration into skin, and geraniol doesnŠ—Èt penetrate skin easily. As such, although itŠ—Ès not a great ingredient to see on a label if you have sensitive skin, it isnŠ—Èt among the most troublesome fragrance ingredients when used in low concentrations. Despite the lesser concern, research has shown that, like many fragrant oil components, geraniol can oxidize in the presence of air, causing damage when appied to skin's surface.
References for this information:
Food and Chemical Toxicology, January 2010, pages 18-23
Chemical Research in Toxicology, May 2007, pages 807-814