aromatherapy diffuser

In addition, there are potential safety concerns. Because essential oils are highly concentrated they can irritate the skin when used neat, that is undiluted.[citation needed]. Therefore, they are normally diluted with a carrier oil for topical application. Phototoxic reactions may occur with citrus peel oils such as lemon or lime.[23] Also, many essential oils have chemical components that are sensitisers (meaning that they will after a number of uses cause reactions on the skin, and more so in the rest of the body). Some of the chemical allergies could even be caused by pesticides, if the original plants are cultivated [24], [25]. Some oils can be toxic to some domestic animals, with cats being particularly prone.[26][27]

Two common oils, lavender and tea tree, have been implicated in causing gynaecomastia, an abnormal breast tissue growth, in prepubescent boys, although the report which cites this potential issue is based on observations of only three boys (and so is not a scientific study), and two of those boys were significantly above average in weight for their age, thus already prone to gynaecomastia.[28] A child hormone specialist at the University of Cambridge claimed "... these oils can mimic estrogens" and "people should be a little bit careful about using these products."[29]

As with any bioactive substance, an essential oil that may be safe for the general public could still pose hazards for pregnant and lactating women.

While some advocate the ingestion of essential oils for therapeutic purposes, licensed aromatherapy professionals do not recommend self prescription due the highly toxic nature of some essential oil. Some very common oils like Eucalyptus are extremely toxic when taken internally. Doses as low as one teaspoon has been reported to cause clinically significant symptoms and severe poisoning can occur after ingestion of 4 to 5 ml.[30] A few reported cases of toxic reactions like liver damage and seizures have occurred after ingestion of sage, hyssop, thuja, and cedar.[31] Accidental ingestion may happen when oils are not kept out of reach of children.

Oils both ingested and applied to the skin can potentially have negative interaction with conventional medicine. For example, the topical use of methyl salicylate heavy oils like Sweet Birch and Wintergreen may cause hemorrhaging in users taking the anticoagulant Warfarin.

Adulterated oils may also pose problems depending on the type of substance used