What characteristic differentiates essential oils from hydrosols?

The correct answer highlights that essential oils are indeed more concentrated and necessitate dilution before application or use. This concentration results from the distillation or expression processes that isolate the volatile aromatic compounds present in plants. Due to this high potency, essential oils can cause skin irritation or sensitization if applied undiluted, which is why it is essential to dilute them properly with a carrier oil or another medium before use on the skin or in formulations.

In contrast to essential oils, hydrosols are the aromatic waters that remain after the distillation of plant materials for essential oils and are typically much less concentrated. They do not require as strict a dilution, making them safer for direct skin application. This distinction underscores the importance of understanding the properties and uses of both essential oils and hydrosols in aromatherapy.

Thus, option B aptly captures a core characteristic of essential oils compared to hydrosols, showing the necessity for caution and proper usage in aromatherapy practices.