Like the digestive system, the reproductive organs can be affected by the absorption via the skin into the bloodstream, as well as through hormonal changes. Some essential oils such as rose and jasmine have an affinity for the reproductive system, having a strengthened effect as well as helping to combat specific complaints such as menstrual problems, genital infections and sexual difficulties. Other oils contain plant hormones that mimic the corresponding human hormones; oils such as hops, sage and fennel have been found to contain a form of estrogen that influences the menstrual cycle, lactation and secondary sexual characteristics.

Other essential oils are known to influence the levels of hormone secretion of other glands, including the thyroid gland (which governs growth and metabolism), the adrenal medulla (which deals with stress reactions) and the adrenal cortex (which governs processes including the production of estrogen and androgen, the male sex hormone).

Virtually all essential oils have bactericidal peroperties, and by promoting the production of white blood cells, they can help prevent and treat infectious illness. It is these properties that gave aromatic herbs and oils such high repute with regard to infections such as malaria and typhoid in the tropics and epidemics of plague in the Middle Ages. 'People who use essential oils all the time . . . mostly have a high level of resistance to illness, catching fewer colds, etc., than average and recovering quickly if they do.'