(please see sources
•Do not take essential oils internally.
•Always use sparingly.
•Lavender and Tea Tree (Melaleuca) are generally safe for direct skin application. Oils that should be applied to the skin with caution, and always diluted, are: Aniseed, West Indian Bay, White Camphor, Clove Bud, Coriander, Eucalyptus Blue Gum, Hyssop, Nutmeg, Sweet Fennel, Parsley Seed, Spanish Sage, Tagetes (only well diluted .05%), Bergamot (well diluted), Verbena, and Thyme.
•Pennyroyal, Mustard, Sassafras, Rue, Wormseed, Tansy, Benzoin, and Mugwort should not be used at all.
Neat (undiluted application).
•As mentioned above, Lavender and Tea Tree are fine for direct application, although some people are sensitive and may develop irritation. If you have sensitive skin, apply a small amount and wait 1 hour. If irritation develops, rub well with pure carrier oil, then wash with soap and water. For future use, try further diluting the oils.
•Oils such as Jasmine, Ylang Ylang and Sandalwood may be applied neat as in a perfume.
•Oils that are known to irritate are: Aniseed, Sweet Basil, Black Pepper, Cajeput, White Camphor, Virginian Cedarwood, Cinnamon Leaf, Clove Bud, Eucalyptus Blue Gum, Ginger, Juniper, Lemon, Lemongrass, Parsley Seed, Peppermint, Pine Needle, Cinnamon Bark, and Thyme. Always use diluted and in small quantities.
•Avoid the following oils before exposure to sunlight or tanning beds: Angelica Root, Bergamot, Lime, Bitter Orange, Lemon, Grapefruit, Sweet Orange, and Tangerine.
•For children and babies, always reduce the recommended amount by half, or more. Definitely avoid any oils that are known to be an irritant. Even Lavender and Tea Tree should be diluted to 1 drop/teaspoon base oil.
•During Pregnancy, only use in half the regular dilution. Totally avoid: Basil, Virginian Cedarwood, Celery Seed, Clary Sage, Clove, Cinnamon Leaf, Citronella, Hyssop, Juniper, Marjoram, Myrrh, Nutmeg, Spanish Sage, and Thyme. During the first four months, avoid Angelica Root, Atlas Cedarwood, Sweet Fennel, Rose, and Rosemary.
•High Blood Pressure. Do not use Rosemary, Spanish Sage, or Thyme.
•Epilepsy. Do not use Fennel, Hyssop, Rosemary, and Spanish Sage.
•Alcohol. Clary Sage can cause nausea and exaggerated drunkenness when used within a few hours before or after drinking alcohol.
•Carcinogenic oils: Calamus, Sassafras.
•Hypoglycemia. Avoid Geranium.
•Kidney problems. Use Juniper, Sandalwood and Coriander with caution.
As with anything, use caution. Buy a quality book, and learn as much as you can about Essential Oils. They have been known to have many medicinal uses and can greatly benefit anyone.
Sources - These safety tips were compiled from various sources including: The Complete Illustrated Guide To Aromatherapy Lawless, The Complete Book of Essential Oils and Aromatherapy Worwood.