Information on safe use of essential oils is based on worldwide research. The concentration of essential oils to be blended with carrier oils for the safe use in Aromatherapy treatments is to use less dosage of essential oils with maximum coverage in the body area applications. 

The usual concentration used of essential oils when blended with base oils is between 2% to 5%. When used over the chest or the abdomen area dosage of 8% to 10% can be used, while areas such as the hands or feet up to 50% may be used. For topical application to a spot certain essential oils can be used in their purest form (100%). But it is very important that the total quantity of concentrate essential oils to be used at one time should not exceed more than 30 drops to 0.5-1.5 ml. This is an adult dosage. But when treating children the dosage has to be decided according to the age and weight of a child. The general guide is to use half a drop of essential oil to each Kg. of the child’s weight. Dosage according to age is as follows : 

12yrs to 16yrs -- 10--15 drops.
07yrs to 12yrs -- 05--08 drops.
03yrs to 07yrs -- 02--03 drops.
01yrs to 03yrs -- 01--02 drops.

ESSENTIAL OILS ARE NOT RECOMMENDED FOR CHILDREN BELOW 12 MONTHS OF AGE.

In Aromatherapy treatment, the frequency of a full body massage is between once a week to once a month but some individuals can have up to three massages a week for a period of time. The health index of a person can be related to the tolerance of using essential oils. Individuals new to Aromatherapy system of treatment need to get accustomed to essential oils.

Essential oils extracted from plants are concentrated (100% pure) and their potency is 100 to 1000 times stronger than in their naturally occurring state. Therefore for the external application, they should be adequately diluted for safety. When properly used, essential oils are beneficial for beauty, mind and body. However essential oils are biologically active substances and its misuse can cause adverse reactions. It is very important to understand that an increase in the concentration of essential oils while treating will not be beneficial. Reaction to oil differs from person to person. Some individuals are hypersensitive and a minuscule amount of essential oil leads to allergy. In such a case, start with a very low concentration and gradually increase to the recommended dose of 2%. 

The Irritation and Sensitisation reactions of essential oils on contact with human skin is carried out with healthy human volunteers. The number of volunteers used in the test ranges from 15 to 75. But on an average, 25 volunteers with no positive reactions is only reliable for 80% of the population according to the international standards. This dose does not mean that the essential oil is proven to be incapable of irritation reaction for the rest of the population. 

Testing for irritation is done by applying the diluted essential oil at a percentage 10 times more than the maximum concentration used in perfumes, on a patch of skin. Usually, it is done on the forearm with a cotton swab for 20 to 48 hours, after which the patch is removed and the skin is examined for an indication of reactions. Patients with skin diseases whenever possible are also tested. 

Like all medicines, pure essential oils should be kept out of reach of children. Individuals who wish to use essential oils are responsible for themselves in their reaction, but when used with the right care and knowledge, great benefit will be derived. 

QUICK REFERENCE LIST: 
ESSENTIAL OILS FOR SKIN APPLICATION
RECOMMENDED DOSAGE FOR USE IN AROMATHERAPY TREATMENTS.

Maximum limit permissible: 20%
Bergamot oil, Rectified.
Camphor oil, White.
Maximum limit permissible: 15%
Lavender oil (Many Aromatherapists use this oil neat).
Lime oil, Distilled.
Maximum limit permissible: 10%
Pine oil, Rosewood oil.
Sandalwood oil.
Patchouli oil.
Spikenard oil.
Ylang Ylang oil.
Rose Mary oil.
Lemon oil, Distilled.
Eucalyptus oil, Globulus.
Geranium oil.
Grapefruit oil, Mild Phototoxic potential.
Sweet Orange oil, Mild Phototoxic potential.
Tangerine oil.
Mandarin oil.
Cinnamon leaf oil.
Tejpat oil.
Bay oil.
Maximum limit permissible: 8%
Ajowan oil.
Lemon Mint oil.
Sage oil.
Spike Lavender oil.
Thyme oil, Red.
Palmarosa oil.
Vetiver oil.
Bitter Orange oil, Mild Phototoxic potential.
Lemon oil, Expressed, Weak Phototoxic potential.
Petitgrain oil.
Guaiac wood oil.
Juniper Berry oil.
Cubeb oil.
Cedarwood oil.
Mace oil.
Myrrh oil.
Frankincense oil. 
Maximum limit permissible: 4%
Spanish Marjoram oil.
Cypress oil.
German Chamomile oil.
Roman Chamomile oil.
Davana oil.
Lemongrass oil.
Cardamom oil.
Galangal oil.
Turmeric oil, Longa.
Ginger oil, Mild Irritation & Phototoxic potential.
Lime oil, Expressed, Strong Phototoxic potential.
Carrot seed oil.
Celery seed oil.
Fennel seed oil.
Dill seed oil.
Spearmint oil.
Peppermint oil, Mild Irritation potential.
Neroli oil.
Caraway oil.
Sweet Basil oil.
Clove bud oil.
Cajeput oil.
Coriander oil.
Myrtle oil.
ALL ABSOLUTE OILS ARE RECOMMENDED AT: 3%
Maximum limit permissible: 3%
Bergamot oil, Expressed.
Rose oil.
Parsley seed oil.
Nutmeg oil.
Cumin seed oil, Strong Phototoxic potential.
Clove leaf oil.
Cade oil.
 
Maximum limit permissible: 1%
Ambrette seed oil.
Angelica seed oil.
Tea tree oil (Many a time used in the pure form by Aromatherapists).
Citronella oil, Irritation potential.
Angelica root oil, Severe Phototoxic potential.
Cassia oil, Moderate Sensitisation potential.
Cinnamon Bark oil, Sensitisation potential.
Maximum limit permissible: 0.25%
Tagetes oil, Irritation & Sensitisation potential.
Verbene oil, Sensitisation & Phototoxic potential.
 
Maximum limit permissible: 0.1%
Costus oil, Severe Sensitisation potential.
According to the author, Costus oil enhances the medicinal properties of the essential oil. Mix a drop to 50mls.
 
Essential oils recommended not for use :
Camphor oil, Yellow & Brown
Savin oil
Chenopodium oil
Sassafras oil
Calamus oil
Mustard oil
Horseradish oil
Bitter Almond oil
Winter Green oil
Boldo leaf oil