Always check oil safety before use, in relation to toxicity, dermal irritation, sensitisation, and phototoxicity.

If you are pregnant, on any prescribed medication or under the care of a GP/clinician, you must seek the authorisation of your GP/clinician before using essential oils.

Diabetes Do not use Eucalyptus, Geranium, Ginger, Angelica and possibly Lemon. These oils lower blood sugar levels.
Epilepsy Do not use Fennel, Hyssop, Peppermint or Sage (all types).
High Blood Pressure (Hypertension) Do not use Rosemary, Sages (all types), or Thymes (all types).

Homeopathic Remedies Please check with your homeopath the oils you cannot use with your remedies. I know you cannot use Black Pepper, Camphor, Eucalyptus or the Mints. Tea Tree, Niaoili and Cajeput are also possibles.
Low Blood Pressure (Hypotension) If you have very low blood pressure, do not use Lavender or Lemon.
Pregnancy No essential oils should be used in the first 3 months of pregnancy. After this time, safe essential oils may be used with consent from your GP or clinician at half strength (not more than 1%). There are many oils that should be avoided during pregnancy, so please always check the safety data before using any. I have noted the oils that I know can be used under the Pregnancy section.

Essential oils are for external use only.
Always dilute essential oils before use, they should never be used neat on the skin.
Always check the safety data of the oils you wish to use and never exceed the recommended dose.
Avoid contact with your eyes. In case of accident, rinse thoroughly with cold water.
If suffering from an infectious disease, wait until the infectious phase has passed before massage is given.
Always ensure that the bottle containing the essential oils has a dropper in it, so that you cannot overdose when adding drops to a bath etc. Some oils are very light and the drops come out quickly, such as Lavender or Mandarin, whilst others are heavier, thicker oils and take a long time, such as Vetivert, so you need to keep your eye on them!
Keep essential oils out of the reach of children.
Essential oils should be kept in dark glass airtight bottles, in a cool temperature and away from direct light. Plastic bottles are only suitable for keeping diluted oils in for a short period of time.
Essential oils are inflammable and explosive. Please don't leave unattended if using in an oil burner.

Flame the Dragon by Amanda Penrose