The circulation of blood around the body is vital to the action in the body of essential oils. Whether they are absorbed through the skin or inhaled (and of course, a certain amount of oil will alway be inhaled during any treatment which involves applying oil to the skin) particles of the oils pass quite quickly into the bloodstream, and this is how they are transported to all parts of the body.

This is true of all substances taken into the body, including nutrients from the food we eat and, most importantly, oxygen from the air we breathe in, which is essential to all the processes that maintain life. In the lungs, stomach, intestines and liver these substances are broken down into forms in which they can be assimilated. The circulatory system is the means by which they reach the individual cells.

Blood circulates in a system of tubes, or blood vessels, of various sizes, arranged in two separate, but interconnected circuits, the smaller of which carries blood between the heart and the lungs, and the larger taking blood around all the rest of the body. In the lungs, oxygen from the air is absorbed into the blood. This bright red, oxygenated blood flows to the heart, from where it is pumped out under pressure to make its circuit round the body. At the same time, the heart pumps blood from which most of the oxygen has been used up back to the lungs.

The blood vessels carrying blood away from the heart are called arteries, and those returning it to the heart are veins. The major arteries and veins connect with a network of smaller vessels, and eventually with the smallest of all, capillaries, which are no wider than a hair. The walls of the arteries and veins are watertight, but those of the capillaries are extremely thin, and allow plasma (the watery part of the blood) and all the nutrients, oxygen and other substances dissolved in it (which may include particles of essential oil) to filter out into the fluid which surrounds the cells. This intercellular fluid can also filter in through the capillary walls, returning the waste products of bodily activities to the blood to be disposed of. It is at the level of the individual cells that the particles of essential oil exert their beneficial effect on the body.

Apart from acting as a transportation system for essential oils, the circulatory system can itself be affected by some oils. Disorders of the circulation, including high and low bloodpressure and varicose veins, are discussed in entries of their own. Rubefacient oils, such as Black Pepper, Juniper, Marjoram and Rosemary, stimulate circulation locally in the area to which they are applied. They cause the capillaries to widen, so a great volume of blood can flow through them. The extra oxygen which this blood flow brings with it helps in many healing processes.

Other oils, most notably Camomile and Cypress, have the opposite effect, and bring about a contraction of the capillaries. This can be useful where there is heat, redness and swelling. Garlic, taken in the form of tablets, capsules or eaten fresh is beneficial to the health of the whole circulatory system and so are Vitamins C and Vitamin E.