Essential Oil Safety: The Rules That Actually Matter
Dilution rates, patch testing, the materials you should never use near the eyes, and the household situations where a diffuser is a bad idea.
Start with dilution, not with the bottle
The single most common mistake with essential oils is using them undiluted on skin. A drop of neat lavender oil is a concentrated chemical, not a mild herb. The working rule is 1-2% for body use, 0.5% for face and around the eyes, and 1% for a room diffuser load. Two drops of oil into a teaspoon of carrier oil is roughly a 1% blend.
Patch test before you commit
Dilute one drop in 5 ml of carrier oil, apply to the inside of the wrist, and leave it for 24 hours. If you react to one oil, you are likely to react to its relatives, so test the whole family before committing to a range.
Know the sensitiser list
Limonene, linalool, citral, geraniol, citronellol, eugenol, iso-eugenol, coumarin and cinnamal are recognised fragrance sensitisers and are declared on cosmetic labels above very low thresholds. This is not a reason to avoid them - it is a reason to dilute properly and to patch test.
Where diffusion is a bad idea
Around babies and young children, around birds and other pets (birds are extremely sensitive to diffused oils, and diffusers are a well-documented risk), in a room with poor ventilation, and anywhere a scented product could mask a safety warning such as a gas leak detector.
Storage is part of safety
Heat and light degrade oils fastest, and oxidation can turn a fine oil into a skin irritant. Keep bottles away from a window, out of the bathroom if it gets steamy, and closed when not in use. 12 months after opening is a sensible household rule.