The following information contains excerpts from my books, Healing with Essential Oils, Essential Oils for the Whole Body and Essential Oils for Mindfulness and Meditation (published by Healing Arts Press, Vermont USA)

Applied appropriately, essential oils are highly beneficial antimicrobial, skin healing, psycho-emotional, pleasant ‘scentual’ agents.  

However, they are highly concentrated volatile organic phyto chemicals, with propensity to be very drying and irritant to skin and mucous membranes.  They rapidly oxidise and degrade, especially if they are not stored correctly, which increases their propensity to cause irritation and sensitivity.  Degradation of an essential oil occurs naturally over time, but is detrimentally exacerbated in the presence of heat and uv light, and when exposed to oxygen, and can result in the oil becoming toxic, sensitising, and corrosive, or, especially in terms of their therapeutic qualities, inert.  

To slow these reactions down and to preserve their optimum quality, essential oils are best stored in a cool dark place, in non-corrosible brown or blue glass, or aluminium, uv protected bottles, with dropper dispensing caps and tightly secured lids.  

Safe Use and Application Guidelines

Storage and care

• Only purchase from reputable suppliers whose oils are ethically and ecologically appropriately sourced, extracted and handled, and who will provide safety data information and details about their chemical composition and source (plant and botanical species, location of growth, and so on).
• Only purchase essential oils stored in amber or dark blue glass bottles with ‘dropper top’ lids (to ensure careful measurement, prevent spillage or accidental ingestion, and to slow down oxidisation). Some suppliers place the essential oil-filled glass bottle in an additional canister, or sleeve, that prevents light infiltration.  This ensures the essential oil is protected from over exposure of UV light.
• Check the sell-by date before use and make a note of the date of purchase (essential oils oxidise rapidly when exposed to oxygen in the atmosphere and UV light, therefore, they have a limited shelf life): 2 years if unopened; 1 year once opened (citrus oils, such as mandarin or lemon, 6 months once opened).  Pine oil’s, and other oils with high terpene content, oxidise rapidly.  Some oils oxidise slowly, for example, sandalwood.
• Discard small amounts of essential oil left in a bottle or container, unless the essential oil is used up rapidly from the moment of first opening the bottle.  NB: do not flush residue or old unused essential oils down the sink or toilet as their oxidised chemicals can be harmful/toxic to fish and the local aquatic micro-biome.
• Replace lids immediately after use (to slow down oxidisation).
• Never ‘top-up’ a bottle of essential oil with more essential oil once opened for use.
• Store in a cool dark place, away from sources of heat and direct sunlight (preferably a fridge – some oils, such as rose Otto, however, will solidify when very cold, but will return to a liquid state at room temperature), to protect the oil from rapid oxidisation (exacerbated by light, heat, and atmospheric oxygen).

Application

• Do not apply essential oils neat to the skin (always dilute in a vegetable oil, non-perfumed lotion or cream – for example, 1 or 2 drops of essential oil to 5ml of vegetable oil).  Undiluted dermal application of essential oils can lead to irritation and sensitisation.  Lavender and Tea Tree essential oils are the exception to this rule (often used as a first aid remedy for insect stings, minor burns or skin abrasions, or mild skin infections), but repeated long term topical application of these oils is not advisable due to the risk of sensitisation.
• Do not swallow or take essential oils internally (see Accidents and Reactions below).
• To avoid sensitisation, do not use the same essential oil or blend of essential oils repeatedly; take breaks from use (every two or three weeks), and vary the essential oils you use if applying them over a long period.  Also, use limited quantities (no more than 6 drops per day).  Essential oils are highly concentrated; very small amounts are very effective.
• Always ensure that the essential oil(s) you select are compatible with your requirement and are otherwise not contra-indicated; especially significant if you are taking prescribed mediation, such as painkillers (e.g. codeine or other opiate derivatives) or blood thinning medication, and so on.
• Wipe up spillages immediately (essential oils will dissolve / damage polystyrene, plastic, varnish, paint, polished and laminated surfaces).

Babies and children

• Do not use essential oils for babies under 3 months old.
• I also do not recommend use of essential oils for infants aged between 3 months and 36 months.  If applied during this age range, they must be used in extreme moderation (1 drop of essential oil in 20ml of carrier medium  – vegetable oil, non-perfumed cream or lotion).  DO NOT use herbaceous, spice, citrus oils (with  the exception of mandarin), or lemon-scented oils (such as, lemongrass or citronella), or highly perfumed oils (such as, Ylang Ylang).  The skin and vital organs of babies are still developing, especially the organs of elimination; essential oils are highly concentrated and can cause a toxic reaction or organ damage in babies and children.
• NEVER, to reiterate, apply undiluted essential oils to a child, infants or babies skin and NEVER add undiluted essential oils to their bath.
• NEVER use essential oils for internal consumption.
• Do not put drops of essential oils directly onto pillows due to the risk of eye contact.
• Keep essential oils out of the reach of children (good suppliers will provide child proof lids if requested) and keep away from pets.
• Essential oils are best diffused into the environment, away from an infants head space to avoid irritation of the airways, perhaps to soothe restlessness, and/or to aid sleep.

Accidents and reactions

• Accidental ingestion: DO NOT INDUCE VOMITING. Drink full fat milk. Seek medical advice immediately. Keep the bottle the essential oil was stored in for identification (the label should display the Latin name, batch no., sell-by date etc., and the bottle will have traces of the oil).
• Eyes: Essential oils can be transferred from your fingers to your eyes (always wash your hands after using or handling essential oils). If NEAT essential oil enters your eyes IMMEDIATELY flush with vegetable oil or full fat milk, then rinse thoroughly with clean, warm water. Sometimes diluted essential oils enter the eyes during steam inhalation, bathing or showering, if this happens immediately flush eyes with clean warm water. In either case, seek medical advice IMMEDIATELY if irritation or stinging persists after flushing your eye(s).
• Skin reaction: Apply vegetable oil to dilute the essential oil on the skin, then thoroughly wash the area with non-perfumed soap (liquid soap if possible) and rinse with warm water to remove any trace of soap and the essential oil.   Dry the area thoroughly and apply a non-perfumed base cream (vegetable oil or even butter if nothing else is available) to soothe irritation if appropriate.

You will find deeper detail about essential oils and their appropriate use and application in my books, Healing with Essential Oils, Essential Oils for the Whole Body, and Essential Oils for Mindfulness and Meditation,