The liver is the largest organ in the body (apart from the skin) and one of the most complex in its actions. It lies on the right side of the body, protected by the lower ribs, and on average weighs about 31bs (1½ kilos) though there can be a lot of variation. The liver has at least four functions which are vital to life: manufacturing, metabolising, storage and detoxification. In addition, because of the continual chemical activity involved in these processes, the liver provides most of the body's heat.

Substances manufactured in the liver include bile, which is needed for the digestion of fats; heparin which helps prevent the blood from clotting, and most of the proteins found in the blood plasma. Vitamin A can be synthesised in the liver from carotene if needed.

A very large part of the liver's activity is concerned with metabolism: i.e. the breaking down of elements from food and converting these into forms in which they can be utilised by the body. Glucose, from sugars and starches, is converted into glycogen which is the fuel used for all muscular activity. Fats cannot be used by the body in the form in which we eat them. In the liver they are oxidised and broken down into simpler forms which can either be used or stored in the liver until needed. Amino acids, which are the 'building blocks' of protein foods, are vital for health, but the body can use or store only limited amounts at any given time, so if too much protein is eaten the liver breaks down the excess by a process called de-amination. Both amino acid residues and fatty acids can also be converted into glycogen and stored.

The storage of glycogen and other nutients in the liver means that they can be released into the bloodstream in regulated amounts as the body needs them. Fat soluble vitamin A and vitamin D are also stored in the liver, and so is iron.

The fourth very important function of the liver is detoxification. In this organ substances that could damage other body tissues, such as a alcohol, drugs and poisons, are broken down into forms in which they can be excreted via the faeces or urine. As well as toxic substances taken into the body, the liver also breaks down and prepares for excretion, substances produced naturally in the body which could cause self-poisoning if they were not removed once their purpose had been served. These include dead red blood cells and hormones. The haemoglobin from red blood cells is converted into pigments that colour the bile, and eventually leave the body in the faeces. When this process goes wrong, the pigments cannot be excreted as fast as they are formed, and they accumulate in the blood and other cells and give the skin a yellow colour — the condition we call jaundice.

A number of essential oils, referred to as hepatic, have a tonic and beneficial action on the liver and strengthen its various actions. By the far the most important of these is Rosemary, which stimulates the production and flow of bile, helps in cases of jaundice and is a general liver tonic. Other helpful oils are Camomile and Peppermint, which benefit the liver and the digestive system as a whole, Cypress, Lemon and Thyme which are useful when the liver is congested, and Juniper as an aid to detoxification.

General body massage or baths with these oils will enable them to enter the bloodstream and reach the liver quite quickly, but relief from discomfort in the liver area is best achieved by means of warm (not too hot) compresses over the liver. In cases of jaundice and congestion, alternating hot and cold compresses, finishing with a cold one, will stimulate the liver and improve its function.

Essential oils which are described as toxic are nearly all capable of damaging the liver to the extent where very serious illness or even death would follow.