Aromatherapy and essential oils: evidence, safety and who should avoid them

Essential oils are concentrated plant extracts. They can be inhaled from a burner, an aroma stick or a tissue, diluted into a carrier for massage, or added in small amounts to a warm bath. Massage sessions with oils commonly last an hour or more.

Because these oils are potent, dilution matters. Undiluted oil on the skin can cause irritation, and oils taken by mouth or placed inside the body can be dangerous, which is why Cancer Research UK states plainly that an essential oil should never be swallowed or put in any other part of the body.

The US National Center for Complementary and Integrative Health says rigorous research on aromatherapy for insomnia is limited and effectiveness remains unclear. In a study of lemon and lavender scents, lemon appeared to improve mood, yet neither scent affected measured stress indicators, immune markers or pain.

Aromatherapy has been used inside massage for anxiety and pain in people with cancer and for knee pain in osteoarthritis, but the NCCIH summary does not rate how strong that evidence is. Cancer Research UK adds that a 2016 Cochrane review found not enough evidence to say aromatherapy massage relieves symptoms, although some smaller studies hinted at benefit for anxiety.

Cancer Research UK flags several groups. People with hormone-dependent cancers are told to be careful because lavender and tea tree oil may affect oestrogen. Pregnant and breastfeeding women, and people with epilepsy, asthma, or kidney or liver disease, are also advised to seek advice first.

Skin sensitivity is another everyday concern. A patch of diluted oil on a small area before wider use is a sensible habit, and stopping at the first sign of redness, itching or breathing difficulty is wise.

• Tell your aromatherapist about pregnancy, epilepsy, asthma and any cancer diagnosis before blends are chosen.

• Keep oils away from children and pets unless a qualified source says it is safe.

• Treat strong scents as possible asthma triggers if you have a history of wheeze.

People with cancer often use aromatherapy hoping to ease anxiety, pain, depression and stress, and Cancer Research UK says the evidence for these effects remains limited. Oils are used either in massage or by inhalation, as described in the application methods above.

Let your cancer team know before you start, especially if you have a hormone-sensitive cancer, because oil choices may need to change.

Cancer Research UK reports that no single regulatory body oversees aromatherapists in the UK. It points to professional organisations such as the International Federation of Aromatherapists and the International Federation of Professional Aromatherapists for finding trained practitioners, ideally with cancer-specific experience when relevant.

The Complementary and Natural Healthcare Council also registers aromatherapy and is approved as an Accredited Register by the Professional Standards Authority. Choosing a practitioner on an accredited register is one way to confirm training and a complaints route, although essential oils sold as retail products have their own, separate rules.