Safe use of essential oils - tolerance test
Essential oils are highly concentrated natural substances and their use requires proper dilution and basic safety precautions. Always perform a patch test before first use to eliminate or minimize the risk of skin irritation or allergic reaction.
How to properly perform a patch test
Patch test (tolerance test)
| Step | What to do | Why is this important? |
|---|---|---|
| 1. Prepare the dilution | Dilute the essential oil in a carrier oil at a concentration of 1–2%. (2 to 5 drops of EO in 5 ml of carrier oil ≈ 1% to 2%). | Undiluted oil can irritate the skin. Dilution simulates normal use. |
| 2. Choose a location | Apply to the inside of the forearm or in the crook of the elbow. | These areas have more sensitive skin and any reaction will appear earlier. |
| 3. Apply a small amount | Apply a pea-sized amount and spread gently. | A small amount is enough to evaluate the reaction. |
| 4. Watch 24 hours | Watch for redness, itching, burning, pimples, or swelling. | Some reactions may occur with a delay. |
| 5. Evaluate the reaction | If significant irritation occurs, wipe the mixture with vegetable oil and wash the skin. | Vegetable oil helps dilute essential oil residue better than water, which essential oils do not mix with. |
A slight, short-term warming sensation (e.g. with spicy oils) may be normal. Severe burning or persistent redness is not common.
Recommended dilution for normal use
| Group | Recommended concentration | Practical example |
|---|---|---|
| Sensitive skin | 0.5–1% | 1 to 3 drops in 5 ml/2–6 to 10 ml carrier oil |
| Adults (common use) | 1-2% | 2–5 drops in 5 ml/4–10 in 10 ml carrier oil |
| Local intensive application (short-term) | max. 3% | 8 drops in 5 ml/16 in 10 ml carrier oil |
The number of drops per 1 ml of essential oil depends on several factors. Generally, an average of about 30 drops per 1 ml of essential oil is used.
Factors on which the size and thus the weight of an essential oil drop depends
- Oil viscosity (density): thicker oils such as patchouli, sandalwood or vetiver form larger droplets because they flow out more slowly, while thinner oils, especially citrus, form smaller droplets.
- Dropper size and type: The diameter of the dropper or pipette hole in the bottle is crucial. A larger hole produces larger drops and vice versa.
- Oil temperature: higher temperature reduces viscosity, the oil becomes thinner and forms smaller droplets. Cold oil is thicker and the droplets are larger.
- Angle of the bottle: The drop is most consistent when the bottle is held vertically, upside down. If the angle is too sharp, the drop may be larger or irregular.
- The amount of oil in the bottle: the level (air pressure inside) can affect the drip rate and thus the size of the drop.
The size of the drop ranges from approximately 0.019, over 0.028 to 0.04 g (essential oils from conifers and woods), i.e. 50, 35 and 25 drops per 1 g of essential oil, which is also a 1% solution if the number of drops is added to 99 g of, for example, carrier oil.
General safety recommendations
| Recommendation | Explanation |
|---|---|
| For external use only | Essential oils are not intended for internal use without professional guidance. |
| Do not use undiluted | High concentration may cause irritation or sensitization. |
| Avoid eyes and mucous membranes. | These areas are significantly more sensitive. |
|
Beware of the sun with citrus |
Some citrus oils may increase skin sensitivity to UV radiation. |
|
Consultations during pregnancy and health problems, |
Some oils are not suitable for specific groups of people. |
| Keep out of reach of children. | Prevent accidental ingestion or improper handling. |
Essential oils unsuitable for regular topical use
| Essential oil | Why is it not recommended locally? | Note |
|---|---|---|
| Cinnamon bark (Cinnamomum verum/cassia) | Extremely dermocaustic, strongly irritating | It is among the most sensitizing oils |
| Cinnamon leaf | High eugenol content – strongly irritating | Only very low dilution and professional use |
| Clove (Syzygium aromaticum L.) | High eugenol content – risk of irritation and sensitization | Not suitable for sensitive skin |
| Oregano (Origanum vulgare) | High content of carvacrol – strongly irritating | Only extremely low dilution (<1%) |
| Thyme, thymol chemotype | High thymol content – irritating | There are more subtle chemotypes (e.g. linalool) |
| Tea tree high in thymol (rare chemotype) | Risk of irritation | Standard Tea Tree is commonly used |
| Mustard oil (e.g. Brassica nigra) | Strongly dermocaustic | They are practically not used in home aromatherapy |
| Ruta (Ruta graveolens) | Strongly phototoxic and potentially toxic | Not suitable for normal use |
| Arnica CO₂ extract | Risk of sensitization | More macerate than EO |
| Sweet birch (Betula lenta) | High methyl salicylate content | Risk of systemic adverse effects |
How to perform a patch test correctly
A patch test is used to verify individual tolerance to a specific essential oil or mixture for topical use. Essential oils are not, with some exceptions, used undiluted on the skin and mucous membranes.
1. Prepare the dilution
Never test an essential oil undiluted (unless specifically instructed otherwise by a professional).
Recommended dilution for the test:
- Sensitive skin: 1% (approx. 2 to 3 drops in 5 ml of carrier oil, i.e. in a teaspoon).
- Normal skin: 1–2% (approx. 2 to 5 drops in 5 ml of carrier oil, i.e. in a teaspoon).
Suitable carrier oils: almond, jojoba, coconut, etc.
Stir the mixture thoroughly.
2. Select a test location
Recommended area: inner forearm or elbow crease.
The area must be clean, dry, and free of irritation or injury.
3. Application
Apply a small amount of the prepared mixture (pea-sized) to the selected area and rub in gently.
Do not cover the site with an airtight dressing unless advised to do so by a healthcare professional.
4. Monitoring time
Monitor the location for 24 hours.
Pay particular attention to any redness, itching, burning, pimples, or swelling.
A mild, short-term warming sensation (e.g., with ginger or spicy oils) may be common. Severe burning or significant redness is not common.
5. Procedure for irritation
If adverse reactions occur:
-
immediately wipe the mixture with vegetable oil (not water), e.g. sunflower, jojoba, almond, etc.
-
Wash your skin with a mild soap and pat it dry.
-
stop using the product,
-
If the reaction persists or is severe, seek medical attention.
You can read about what essential oils are in our article , and we have written instructions for using these natural products.
The article was written by Mgr. Radka Příkopová Brichcínová, Master of Pharmacy, on February 16, 2026.
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