Catechol (the preferred chemical name) has about a third the toxicity of pyrogallol. Still it is considerably more dangerous than hydroquinone. This may be because the human body uses a group of chemicals known as catecholamines and catechol may interfere with their use. Catechol has a measureable vapor pressure at room temperature and the solid should be used with adequate ventilation. It has a distinctive phenolic odor reminiscent of the smell of an old-time drugstore.