Some essential oils cause strong irritation or even burns to the skin and mucous membranes. Indeed, some essential oils are likely to attack, or even destroy, the skin or mucous membranes. They are said to be dermocaustic.
The reactions that can occur as a result of skin contact with an essential oil are variable and depend on several factors. These reactions of an inflammatory nature are also called dermatitis. They are three types:
- Irritation is a reaction that occurs quickly after contact. It usually goes away after a few hours. The severity of this type of reaction depends on the dilution.
- Contact allergy (or sensitization) does not occur immediately after contact. It is the result of the immune system response. That’s why these reactions vary greatly from person to person.
- Photosensitization occurs when essential oil applied to the skin is exposed to natural or artificial ultraviolet rays. Phototoxicity, which you can find in an other post, is a form of photosensitization.
An irritating essential oil: causes inflammation of the skin resulting in redness, itching and/or a feeling of heat.
A dermocaustic essential oil: causes strong irritation, even a burn of the skin and mucous membranes.
Which molecules are at risk from dermocaustics?
These are the oils that contain phenols (Carvacrol/Thymol) and aromatic aldehydes Cinnamaldehyde.
Dermocaustic essential oils with phenols
- Dill (Anethum graveolens)
- Ajowan (Trachyspermum ammi)
- Tropical basil (Ocimum basilicum var. basilicum)
- Bay or Bay of St Thomas (pimenta racemosa)
- Tarragon (Artemisia dracunculus)
- Thyme (Thymus serpyllum)
- Thyme (Thymus vulgaris ct thymol and ct carvacrol)
- Ajowan (Trachyspermum ammi)
- Clove (Eugenia caryophyllus)
- Mountain savoury (Satureja montana)
- Compact oregano (Origanum compactum)
- Oregano from Greece (Origanum heracleoticum)
- Oregano from Spain (Corydothymus capitatus)
Dermocaustic essential oils with aldehydes
- Verbena (Lippia citriodora) EO
- Lemony Litsea (Litsea citrata) EO
- Lemongrass (Cymbopogon citratus and flexuoxus) EO
- Ceylon and Chinese cinnamon (Cinnamomum zeylanicum and Cinnamomum cassia) EO
How to use them
To avoid skin damage with dermo-caustic essential oils, take the following precautions:
– should not be used pure on the skin
– must be diluted with a VO before skin application (maximum dilution of 3% (Example for 10 ml of VO do not exceed 9 drops of EO),
– do not take them orally because even diluted in oil, honey or other they can still irritate the oesophagus.
– Always do an allergy test, in the bend of the elbow
The authors of Essential Oil Safety indicate the maximum dilutions to apply to ensure that the risk of dermo-causticity becomes low.
To note:
Essential Oils of mustard (brassica nigra), onion (Allium Cepa) and also garlic (Allium sativum) can cause the destruction of the skin, there is no safety threshold. As a result, their use is strongly discouraged and should only be recommended by experienced aromatherapists.
Particular case:
Peppermint EO (Mentha piperita) is also caustic for the skin, its refreshing action can cause colds or thermal shocks even diluted if used on important parts of the body or in the bath. The maximum amount of essential oil applicable per day
The authors of Essential Oil Safety present a gradation table of the risks of skin irritation with the maximum levels of dilution. To establish these percentages, they considered that the maximum amount of product that can be applied in one day is 30 ml.
High-risk essential oils
Per day
| EO | Max dilution for a mixture of 30 ml | Max quantity for a skin application (ml) | Equivalent in nb of drops |
| Black mustard (Brassica nigra) |
No safe threshold |
||
| Massoia (Cryptoria massoïa) |
0,01 % |
0,003 ml |
0,1 |
| Cinnamon (Cinnamomum zeylanicum) |
0,07 % |
0,021 ml |
0,5 |
| Garlic (Allium sativum) |
0,1 % |
0,03 ml |
0.75 |
| Clove bud (Eugenia caryophyllum) |
0,5 % |
0,15 ml |
3.75 |
| Oregano (Origanum compactum) |
1,1 % |
0,33 ml |
8 |
| Savory (Satureja montana) |
1,2 % |
0,36 ml |
9.75 |
| Thyme thymol (Thymus vulgaris CT thymol) |
1,3 % |
0,39 ml |
24 |
| Ajowan (Trachyspermum ammi) |
1,4 % |
0,42 ml |
10.5 |
Calculation basis: 1 ml = 25 gouttes.
Sources :
- Tisserand, R. Young, Essential Oil Safety, 2nd ed., Churchill Livingstone-Elsevier 2014
