Eucalyptus oil is oil distilled from the leaves of the eucalyptus tree (Eucalyptus globulus), an evergreen known for its fast growth. Although the eucalyptus tree is native to Australia, it is now grown all around the world.

According to a 2016 study, eucalyptus oil has antimicrobial, antifungal, and herbicidal properties.

Advocates of using eucalyptus oil to apply to hair suggest that it:

Before using eucalyptus oil, proceed carefully. Like most essential oils, it’s important to dilute eucalyptus oil in a carrier oil before applying it directly to the skin.

A 2010 study concluded that eucalyptus oil has anti-inflammatory properties. Although not proven by clinical research, advocates of eucalyptus oil for hair believe that the oil can reduce scalp inflammation to create an ideal environment for hair growth.

It’s estimated that dandruff and related seborrheic dermatitis affect about half of the adult population. A 2012 report published in the Asia Pacific Journal of Tropical Disease indicated that eucalyptus oil has antifungal and antiseptic properties that can act as an anti-dandruff treatment.

If you are involved in an outbreak of head lice, you might consider eucalyptus oil as a possible treatment.

A 2017 Australian study concluded that the efficacy, safety, and ease of using eucalyptus oil (in a solution with Leptospermum petersonii) make it a productive alternative in the treatment of head lice.

Before using eucalyptus for head lice, check with your doctor, who may have other suggestions for treatment.

Piedra is a fungal infection that results in nodules forming on the hair shafts. Nodules from white piedra are typically found in facial and body hair. Nodules from black piedra are typically found in scalp hair.

Eucalyptus oil, according to a 2012 study, proved effective against the fungus Trichosporon ovoides behind the infection.

There has been a fair amount of clinical research done on eucalyptus oil. And some of it applies to hair, such as its effects on dandruff, head lice, and piedra. There are other claims about the oil — such as promoting hair growth — that have not been clinically proven.

If you are considering adding eucalyptus to your hair-care routine, remember that if it’s not diluted, it could be unsafe. If you have concerns about if to use it or how to use it, talk to your doctor or dermatologist.