Under certain conditions, even the most beneficial essential oils can prove harmful. Concentrated oils are very strong, and just because a product is ‘natural’, that does not mean it’s harmless. Inappropriate use can sometimes lead to adverse or damaging side effects. This is a partial list of medical concerns that warrant avoiding some oils. If you are aware of other contraindications that we’ve omitted, please email us.

Partial List of Conditions that Warrant Avoiding Some Oils

Pregnancy: Essential oil use during pregnancy is a subject about which there is much discussion and disagreement. Some professionals believe that most or all essential oil use should be avoided in the first trimester of pregnancy (the most critical period of fetal development). However, many pregnant women suffering from morning sickness or nausea during the first trimester do not wish to use pharmaceuticals. Often, they can be helped by simply inhaling ginger CO2 or a citrus oil with no known risk to the fetus. Any pregnant woman who wishes to use essential oils during pregnancy, though, should first check with her obstetrician to ensure there are no medical contraindications to doing so.

For pregnancy in general, we suggest avoiding Basil, Cedarwood, Clary Sage, Coriander, Hyssop, Jasmine, Juniper Berry, Sweet Marjoram, Oregano, Myrrh, Peppermint (which in many cases should also be avoided while breastfeeding), Rockrose, Rosemary, Sage, and Thyme.

If you suffer from a seizure disorder: avoid Basil, Fennel, Hyssop, Rosemary, and Sage.

If you have diabetes/hypoglycemia (low blood sugar): some sources say to avoid Geranium.

If you have high blood pressure, it is suggested to avoidPine, Rosemary, Sage, and Thyme.

Kidney/renal problems: should cautiously approach the use of Juniper Berry, Sandalwood, and Coriander.

Blood thinner/anticoagulant use: (including Aspirin, Coumadin, Eliquis, Brillinta, Xarelto, Lovenox, Heparin, etc.) If you are on anti-coagulant therapy (blood thinners), you should avoid oils high in eugenol, including Clove Bud, Cinnamon Leaf, Cinnamon Bark, Wintergreen, and Bay Laurel (Pimenta racemosa). Two oils with almost identical components that are considered dangerous to use are Birch (Betula lenta) and Wintergreen. They have their own page with warnings about them.

Some of the above cautions listed apply only to ingested oils (that is, oils taken internally-more on that later), but a few cautions apply to all routes of administration (inhaling, skin application, and internal use). Other aromatherapy professionals say that such cautions are completely unfounded, having no clinical evidence to support the claims. In short, there are no “one-size-fits-all” guidelines. This is why we suggest consulting with a trained aromatherapist who can help make suggestions according to *your* personal situation.


Photosensitivity refers to dermal (skin) application of certain essential oils with the areas of skin then exposed to the sun’s rays within 12 hours of application. This can result in reddening, dark pigmentation, or skin blistering. Strongly photosensitizing oils include Bergamot (furanocoumarin-free/FCF bergamot is not phototoxic), expressed/cold pressed Lime, and Rue. Cumin, Mandarine, Lemon, Tangerine, Sweet and Blood Orange and Verbena are considered moderately sensitizing. Angelica Root, Caraway, Cassia, Cinnamon Bark, Grapefruit, Honeysuckle Absolute, Laurel Leaf Absolute, and Patchouli are mildly sensitizing, and Virginia Cedarwood, Dill Weed, and Petitgrain are considered very mild on the photosensitizing scale.

Any cold-pressed citrus oil can be considered a potential photosensitizer. Steam-distilled citrus oils, on the other hand, do not carry this risk. St. John’s Wort CO2 and its infused oil can also be photosensitizers.

Substance Use and Essential Oils

Clary sage essential oil should not be used when consuming alcohol, because it may increase alcohol’s sedative effects. Sweet Marjoram and the Chamomiles can also cause drowsiness. In general, if you use or plan to use pharmaceuticals with sedative effects like opioid medication, or other mind-altering substances known to cause drowsiness, you should consider avoiding use of these essential oils.

Sensitizing Oils (oils which can cause permanent adverse reactions)

Sometimes, sensitization can be caused by overuse of essential oils. Some aromatherapists in the past, for instance, poured their oils without using safety equipment such as gloves, safety glasses, and lab coats, and a well-ventilated area. After a while, they found that whenever a particular oil (say lavender) was being poured, they coughed, sneezed, suffered difficulty breathing, broke out in skin rashes, or suffered other uncomfortable symptoms. In other words, they had become sensitized to that oil. For a more complete description of sensitization, click here.

The following essential oils have either a proven or suspected history of causing sensitization (allergies): Aniseed, Bay, Benzoin, Balsam of Peru (VERY HAZARDOUS), Calamus, Cardamom (suspect), Cassia, Cinnamon Bark and Leaf, Citronella, Clary Sage (suspect), Costus, Dill Seed (not dill weed), Fennel (Bitter, not sweet), Fig Leaf Absolute, Galbanum Resin (cross-sensitizing with Peru Balsam), Hyacinth Absolute (suspect), Jasmine Absolute, Juniper (suspect), Laurel (Bay Laurel), Lemon (suspect), Litsea Cubeba (suspect), Lovage (suspect), Mimosa Absolute, Oakmoss Concrete (suspect), Orange (suspect), Pines (suspect), Rose Absolute (if used in high concentrations), Spearmint, Tolu balsam (VERY STRONG), Tagetes, Turpentine, Lemon Verbena (the IFRA strongly advises against the use of Verbena oil in cosmetics or perfume products), and Ylang ylang (in very high concentrations). Source: Tisserand and Young’s Essential Oil Safety, 2nd edition.

NOTE: Some oils should not be used except by clinically trained aromatherapists. Among them are Birch, Dalmatian Sage, Thuja, and Wintergreen.

To read more about possible negative reactions to aromatic chemicals, click here. To read if Benzoin is a Safe Preservative, click here.

Carcinogenic Oils

Essential oils which contain known carcinogenic components are Calamus (European and Asian) and Sassafras. (Please note: Sassafras essential oil is banned for use in cosmetics and toiletries in all of Europe. We do not offer it at Nature’s Gift.)

Potentially Dangerous Effects

Some essential oils have such potentially dangerous effects that it makes them too risky to experiment with. The oils on our personal “to be avoided at all costs” list are: Bitter Almond, Calamus (grown in Europe or Asia, the Canadian/USA grown is safer), Yellow Camphor, Horseradish, Mugwort, Mustard, Rue, Sassafras, Southernwood, Tansy (other than Annual/Blue Tansy), and Wormwood.

Unsafe Methods of Use

A method of using essential oils (promoted by certain multilevel marketing (MLM) corporations that flies in the face of all established safety guidelines is called Raindrop Therapy. For a white paper that discusses the risks, click here.

In professional aromatherapy practice, there are rarely any “no, never” cautions. However, one area where we never, ever recommend essential oil use is in the eye. The risk of damage to these delicate organs is too great and therefore we do not advocate use of essential oils in the eyes. For more information, click here.

Can Essential Oils Be Used Internally?

We do not make claims that essential oils can be used internally. In fact, our labels clearly state “not for internal use”. Why? At least two large multi-level marketing (MLM) essential oil companies have carelessly recommended gross overuse of these powerful substances. Some people think nothing of adding multiple drops of essential oil to a glass of cold water or cup of hot tea. In their minds, it’s the same as drinking an herbal tea or flavored water. In actuality, they’re drinking the equivalent of quarts of tea/flavored water in that one cup of water.

Also, essential oils and water do not mix, no matter how much you shake a bottle with water and essential oil in it. Undiluted molecules of powerful essential oil will come in contact with the delicate mucus membranes of the mouth and the lining of the esophagus and stomach.

In rare cases, essential oils may be used internally. Some of us with specialized training in aromatic medicine have used our oils internally, upon rare occasion, and with great respect for their power. The ancient Greek term “pharmakopea” has two meanings…“medicine” and “poison”…because anything powerful enough to heal is also powerful enough to do damage. Internal use of essential oils should be overseen by a practitioner trained and skilled in the modality.

In all but the most complicated cases, internal use is NOT the most advantageous way to reap the benefits of essential oils. Inhalation and properly diluted skin application are perfect for the vast majority of concerns.

Occasionally, we will cook with a drop or two of essential oil which is well-diluted in fat contained within the recipe. A jar of honey with a drop or two of ginger oil in it to add to tea for health reasons is an acceptable practice…two drops of ginger essential oil in an 8 ounce jar of honey is plenty enough for good results. This rare and “respectful” use of essential oils goes against the willy-nilly, “all the oils all of the time” use recommended in many aromatherapy groups on the Internet.