�?If harvesting herbs from the wild only take what you need and only if the plant is growing abundantly - however, some plants are protected and must never be picked, so be sure to never pick rare or uncommon plants from the wild.
�?Do not harvest bark from the wild - if you are harvesting bark from a tree in your garden be sure to never take a complete strip going around the trunk / branch as this will prevent nutrients from rising up the tree and you may kill the tree! Avoid over-stripping, preferably taking it from a peripheral limb which can be cut back. Harvest you sap in Spring when the sap rises, or Autumn as the sap falls.
�?Consider where the plant has been growing and whether it could be contaminated by pollution.Avoid plants growing along roadsides, close to factories, in built-up areas or where crop spraying occurs.
�?And of course... make sure you identify the plant correctly! It's an easy mistake to make - if you're ever in doubt, the safest thing to do is not use it. Even some herbs sold over the counter have been mistakenly identified - always make sure you purchase your herbs and oils from a reputable source!

�?When working with essential oils [blending your own oils for example] make sure you drink plenty of water to keep you hydrated; clear up any spills immediately; work in a well ventialated space; and remember to take breaks!

Hazardous Oils
The following oils are generally considered unsafe for use in aromatherapy and self-treatment. The list includes those which are known to be narcotic, toxic, cause damage to the skin, provoke fits, or are capable of causing a miscarriage. Trained medical professionals and homeopaths may well use some of these herbs and oils in minute amounts, but these oils should never be used in self-treatment or aromatherapy.

Aniseed - Pimpinella anisum - Relatively high toxicity, and is also addictive.
Arnica - Arnica montana - The essential oil of arnica is highly toxic. However, the tincture, and Arnica cream/ointment, readily found in health-food shops and chemists, is perfectly safe for external use and has many benefits.
Bitter Almond - Prunus amygdalis, var. amara - Contains cyanide. The Almond oil used as a carrier oil comes from the Sweet Almond and is perfectly safe.
Boldo Leaf - Peumus boldos - Extremely toxic.
Calamus - Acorus calamus - Possible carcinogenic.
Camphor - Cinnamomum camphora - Brown and Yellow Camphor are toxic and carcinogenic and should not be used. White Camphor is considered relatively non-toxic - it is however an enviromental hazard or marine pollutant.
Cashew - Anarcardium occidentale - The shell oil and its vapour are highly irritant and should not be used in any form.
Chervil - Anthriscus cerefolium - Toxic and irritant. Possible carcinogenic.
Cinnamon Bark - Cinnamomum zeylanicum - Essential oil from the bark is a very strong skin irritant - the leaf offers a slightly safer oil, although it is still an irritant and should only be used with caution [in small amounts and well diluted!]. The leaf oil smells more like cloves, and the bark oil smells like cinnamon.
Costus - Sausserea lappa
Cotton - Gossypium herbaceum - Cotton root bark and seed oil are potentially toxic.
Horseradish - Cochlearia armorica, Armoracia rusticana
Jaborandi Leaf - Pilocarpus jaborandi
Melilotus - Melilotus officinalis
Mugwort [Armoise] - Artemisia vulgare - Toxic, high thujone content, abortifacient.
Mustard - Brassica nigra - Considered one of the most toxic essential oils.
Origano - Origanum vulgare - A powerful emmanagogue [avoid during pregnancy] and a fairly severe skin irritant. The closely related Marjoram [Origanum majorana] is a far safer oil to use.
Origano [Spanish] - Thymus capitatus
Pennyroyal [European] - Mentha pulegium - Presents a risk of poisoning.
Pennyroyal [N. American] - Hedeoma pulegioides - Presents a risk of poisoning.
Pine [Dwarf] - Pinus pumilio or Pinus mugo - Several species of Pine are used to yield essential oils - not all of them are hazardous, but be sure you know which one you are using, and avoid Dwarf Pine.
Rue - Ruta graveolens
Sage - Salvia officinalis - There have been a number of cases of hospitalisation following the self-administration of Sage essential oil. Clary Sage [Salvia sclarea] is generally used as a safer alternative [although Clary Sage should never be used with alcohol as it will cause nightmares!]
Sassafras - Sassafras albidum - Presents a risk of poisoning.
Sassafras [Brazilian] - Ocotea cymbarum - Highly toxic, carginogenic, irritant, abortifacient.
Savine - Juniperus sabina
Savory [Summer] - Satureja hortensis
Savory [Winter] Satureja montana
Southernwood - Artemisia abrotanum
Spanish Broom - Spartium junceum - Toxic
Sweet Birch - Betula lenta - Presents a risk of poisoning.
Tansy - Tanacetum vulgare
Thuja [Cedarleaf] - Thuja occidentalis - Presents a risk of poisoning.
Thuja Plicata - Thuja plicata - Presents a risk of poisoning.
Wintergreen - Gaultheria procumbens - Toxic, irritant, sensitising. Also considered an enviromental hazard or marine pollutant.
Wormseed - Chenopodium anthelminticum - Considered one of the most toxic essential oils.
Wormwood - Artemisia absinthium - Toxic, abortifacient.

Oils to use with Caution
The following essential oils should be used in moderation and with caution. Some of the oils have a risk of toxicity. If you do use any of these oils, use them in moderation and only for a few days at any one time.

Basil - Ocimum basilicum
Bay Laurel - laurus nobilis - Possible narcotic properties, use in moderation.
Cedarwood - Cedrus atlantica
Cinnamon Leaf - Cinnamomum zeylanicum
Eucalyptus - Eucalyptus globulus
Fennel [Sweet] - Foeniculum vulgare
Hyssop - Hyssopus officinalis
Lemon - Citrus limonum
Nutmeg - Myristica fragrans
Orange - Citrus aurantium
Parsley - Petroselinum sativum - Moderately toxic and irritant, use in moderation.
Star Anise - Illicium verum - Narcotic in large amounts, use in moderation only.
Tarragon - Artemisia dracunculus - Moderately toxic, possible carginogenic, use in moderation.
Thyme - Thymus vulgaris
West Indian Bay - Pimenta racemosa - Moderately toxic, can lead to cerebral disorders. Use in moderation only.

Photosensitising Oils
The following oils should not be used on skin before exposure to the sun [or a sunbed] as they increase the skin's sensitivity to UV light, which could result in severe burns. There is some evidence to suggest that the photosensitising effect of some oils does not occur if the oils are diluted to less than 2% [P.Davis] but unless there is a real therapeutic need for them, it would be wiser to avoid using them if you intend to be out in strong sunshine.

Angelica - Angelica archangelica
Bergamot - Citrus bergmia
Cumin - Cuminum cyminum
Lemon - Citrus limonum
Orange - Citrus aurantium

Other citrus oils such as Tangerine, Mandarin, Lime [expressed 'peel' oil], Citronella and Sweet Orange have not been proved conclusively to be photosensitisers - but should perhaps be used with caution when exposing skin to UV light. Whilst Grapefuit does contain some of the Furocoumarins that have a photosensitising effect, research has shown that one or more of the other constituents appear to have a neutralising effect.

Herbs which can increase sensitivity to sunlight include :
Bishop's Weed - Ammi majus - Can cause an allergic reaction to sunlight.
Fig - Ficus caria - The milky latex from the stems and leaves may cause an allergic reaction to sunlight when applied to skin.
Masterwort - Imperatoria ostruthium - may cause an allergic reaciotn to sunlight if applied to the skin.
Rue - Ruta graveolens - May cause an allergic skin reaction to sunlight if taken internally.
St John's Wort, Y Fendigedig [Welsh] - Hypericum perforatum
Turmeric - Curcuma longa, C. domestica - if you are taking medicinal doses of Turmeric avoid over-exposure to the sun.

Skin Irritants
If you suffer from sensitive skin you may find that many oils irritate your skin if not diluted enough - generally speaking most essential oils are perfectly safe used in a 3% dilution [for massage blends], less for people with sensitive skin, children and elderly people with frail or thin skin. However, there are some oils which are best used in no more than a 1% dilution - and others which shouldn't be used on the skin at all, but these are included in the Hazardous Oils list.
Always dilute the following oils to 1% before using them on your skin :

Allspice [Leaf and Berry] - Pimenta diocia
Angelica - Angelica archangelica
Bay Laurel - Laurus nobilis
Black Pepper - Piper nigrum
Cinnamon Leaf - Cinnamomum zeylanicum [Essential oil from Cinnamon Bark should never be used on the skin - it is much more of an irritant than oil from the leaf].
Citronella - Cymbopogon nardus
Clove [All parts] - Eugenia caryophyllus
Ginger - Zingiber officinalis
Lemon - Citrus limonum
Lemon Balm - Melissa officinalis
Lemongrass - Cymbopogon citratus
Lemon Verbena - Lippia citriodora
Orange - Citrus aurantium
Nutmeg - Myristica fragrans
Peppermint - Mentha piperata
Scotch Pine - Pinus sylvestris - Avoid in allergic skin conditions

Herbs which can cause skin irritation or contact dermatitis include :
Agave - Agave americana - External use may cause skin irritation
Cabbage - Brassica oeracea - A cabbage poultic may cause blisters if left on for several hours.
Elecampane - Inula helenium- Can cause skin reactions.
Marjoram [Wild] - Origanum vulgare - External use may cause irritation of the skin.
Mayweed, Stinking Mayweed - Anthemis cotula - All parts of this plant can cause blistering if applied fresh to the skin.
Peruvian Balsam - Myroxylon balsamum - May cause allergic skin reactions.
Polypody - Polypodium vulgare - may cause a skin rash when applied externally.
Rue - Ruta graveolens - The fresh plant may cause dermatitis - wear gloves if handling it.
Scots Pine - Pinus sylvestris - Do not use if prone to allergic skin reactions.
Skunk Cabbage - Symplocarpus foetidus - Handling fresh skunk cabbage may cause the skin to blister.
Turmeric - Curcuma longa, C. domestica