Four things never to do

Essential oils are concentrates. A single drop of lavender oil holds as much of the plant's aromatic material as a large quantity of fresh flowers, and that concentration is the reason for care.

The four points below are situations described again and again in the literature on household accidents. They are not gentle suggestions.

One — never in the eyes, the inner ear or on mucous membranes

Essential oils do not dissolve in water and do not rinse away easily with it.

If oil gets into an eye: rinse immediately with clean water, continuously, for at least fifteen minutes. Tilt your head towards the affected side so the water does not run into the other eye, blink while rinsing, and do not rub. Then go to a medical facility and take the bottle with you.

Do not stop to look for saline. Clean tap water will do, and speed matters more than the kind of liquid.

You may come across advice to put a carrier oil into the eye instead of rinsing with water, on the grounds that essential oils repel water. That advice does exist in some aromatherapy literature, but it is not a first-aid protocol. The guidance of Vietnam's Poison Control Centre and of eye hospitals is to rinse with water — because missing the first fifteen minutes is more dangerous than an imperfect rinse, and because cooking oil is not sterile.

Two — never apply neat to the skin

Applying an undiluted oil causes irritation and, more seriously, sensitisation — the body learns to treat that substance as an allergen, and later reactions are stronger than the first.

Sensitisation goes one way. Once it has happened the reaction usually lasts, and you should not deliberately test that substance again. Reactions sometimes fade after many years, but that is not something worth testing on yourself.

The dilution rules are on the next page.

Three — never swallow, and never add to food or drink

This is the clearest line of all. In Vietnam essential oils are regulated as cosmetics, and cosmetics have no oral route of use.

To put our own position plainly: what we sell is not for drinking. Some bottles on the market are sold as food or flavourings; that is a different class of product with different paperwork — do not reason from one bottle to another.

Some oral uses do exist in medicine in a few countries, but they sit within the prescribing scope of licensed professionals, with their own doses and preparations. That is not something to do at home, and not something we advise on.

Four — keep out of reach of children

Essential oils look like water and smell appealing. Swallowing one is an emergency, especially oils rich in camphor or menthol.

If a child swallows oil: do not induce vomiting, keep the bottle so you know what it was, and go to a medical facility at once.

A child-resistant cap is the smallest investment in this whole business.