What are essential oils?

bottle of essential oil with oil dripper

Essential oils, which are obtained through mechanical pressing or distillation, are concentrated plant extracts that retain the natural smell and flavor of their source.

Each essential oil has a unique composition of chemicals, and this variation affects the smell, absorption, and effects on the body. The chemical composition of an essential oil may vary within the same plant species, or from plant to plant.

Synthetic oils are not considered true essential oils.

Have researchers studied essential oils?

Previous studies have shown that lavender and tea tree oil may act as endocrine disrupting chemicals (EDCs), which have been associated with several health issues. EDCs are substances in the environment (air, soil, or water), food sources, personal care products, and manufactured products that interfere with the normal function of your body’s endocrine system. Also, clinical research found a possible link between the topical use of essential oils and the onset of male gynecomastia, or the development of breast tissue, in prepubescent boys. Since lavender and tea tree oil are composed of hundreds of chemicals, NIEHS scientists wanted to find out which of these chemicals displayed hormonal activity that could potentially lead to prepubertal gynecomastia.

What is NIEHS Doing?

How did NIEHS researchers conduct the 2007 study on lavender oil and tea tree oil?

The scientists applied pure essential lavender oil, tea tree oil, or eight of their chemical components to human cell lines in test tubes, known as in vitro experiments. They found that the compounds displayed a range of hormonal activities, which may stimulate prepubertal gynecomastia in boys.

Which essential oils and components were tested in the NIEHS study?

The researchers tested pure essential lavender and tea tree oils, as well as four chemicals commonly found in both: eucalyptol, 4-terpinenol, dipentene/limonene, and alpha-terpineol. These compounds were selected because the International Standard Organization mandated that they be included in both lavender and tea tree oils. The NIEHS research team also studied linalyl acetate and linalool, which are specific to lavender oil, and alpha-terpinene and gamma-terpinene, which are specific to tea tree oil.

Do other essential oils contain these chemicals?

According to an analysis of the chemical components of 93 essential oils, the eight chemicals selected in the NIEHS study appeared in most, as indicated in the list below. Each of the eight chemicals is followed by the number of oils in which it appeared.

  • dipentene/limonene – 90
  • alpha-terpineol – 87
  • linalool – 82
  • 4-terpinenol – 80
  • eucalyptol – 79
  • gamma-terpinene – 79
  • alpha-terpinene – 77
  • linalyl acetate – 62

What age range are boys at risk for gynecomastia?

Male gynecomastia is a common clinical symptom observed during infancy, adolescence, and older age. Some physicians theorize that periods of major hormonal change may lead to the condition. However, prepubertal gynecomastia is relatively rare due to lower circulating hormone levels. Some scientists suspect that boys in this range may be more susceptible to hormonal changes and disrupting chemicals, which may lead to gynecomastia.

Is direct skin exposure the main link to male gynecomastia or can smelling or inhaling essential oils, as in aromatherapy, be linked, too?

The clinical cases have only described using essential oils on skin or topical exposure and not aromatherapy. In the NIEHS study, the team described whether topical exposure to the chemicals led to hormonal activity. Further studies are needed to determine if the same can be said about aromatherapy.

Are girls affected by lavender and tea tree oils?

Because breast growth is a natural process for pubescent girls, it is more difficult to determine whether pure essential lavender oil or tea tree oil have the same effect in females as males. A clinical case was reported in 2019 that described abnormal breast growth in prepubescent girls who had continuous exposure to lavender-fragranced products. The premature breast growth resolved when exposure to the lavender-containing products stopped.

What were the results of tests using pure essential oils?

NIEHS researchers created different dilutions of the two types of pure essential oils and the eight selected chemical components and tested their activity. They found as the dilution increased, the EDC activity of the oils and chemicals decreased.

Should the public discontinue the use of essential oils? Why or why not?

Using essential oils is up to the individual. The researchers want the public to be aware of the findings, since some essential oils and their components display hormonal activity and could be potential EDCs.

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)