Five aromatic constituents of essential oils (cineole, citral, geraniol, linalool and menthol) were tested against twelve fungi (three yeast-like and nine filamentous).

The citral and geraniol oils were the most effective (inhibiting all twelve fungi), followed by linalool (inhibiting ten fungi), cineole and menthol (each of which inhibited seven fungi) compounds.

Both the citral and geraniol containing oils are classified as aldehydes - the cleaners of aromatherapy.

Citral (inhibits 12 fungi) is an aroma compound used frequently in the perfume industry for its citrus effect. It’s also used as a food flavor and  to fortify the effects of lemon oil.

Additional to Citral’s potent anti fungal qualities, it is frequently used as an insecticide. It is also a great fat burner and excellent for promoting weight loss. Citral if often used for making weight loss medications. A great deodorizer, citral is frequently used to mask the smell of smoke. High citral content makes an oil more of a potential skin irritant.

Percentage of citral content in 5 essential oils

Lemongrass (Cybopogon flexuosus & C. Citratus) - 70–80%
Lemon Tea Tree (Leptospermum petersonii) - 70-80%
Petitgrain (Citrus aurantium) - 36%
Lemon balm (Melissa officinalis) - 13%
Lemon (Citrus limon) - 2-5%
Orange (Citrus sinensis)- 2-5%

Geraniol (inhibits 12 fungi) is an aroma commonly emitted by the flowers of many plant species. It is commonly used by food, fragrance and cosmetic products. A common component of rose, palma rosa and geranium oils, it is also an important fragrance compound of  ginger and lavender.

Percentage of Geraniol Content in 5 Essential Oils

Palma rosa (Cymbopogon martinii) - 85-92%
Rose (Rosa damascena) - 35%
Rose geranium (Pelargonium graveolens & P. roseum) - 20%
Lavender (Lavandula angustifolia) - 5.3%
Ginger (Zingiber officinalis) - 5%

Next we have Linalool which is classified as a monoterpenol. Monoterpenols (a subclass of Alcohols) - are the female athletes of aromatherapy.

Alcohols are known to promote enhanced synergistic effects. Synergism is a very important quality for an oil to have, as it boosts the effect of a single oil in its action, especially when in combination with other essential oils, botanical plants and extracts, or even when used with pharmaceutical agents. 

Monoterpenols are found in most essential oils and are generally nontoxic. Essential oils rich in monoterpenols strengthen the immune system and are great for skin care. They promote emotional balance and calm nervous energy, anxiety and stress.

Linalool (inhibits 10 fungi) gives a floral, spicy aroma and is found in many well known  floral and citrus oils. In fact, linalool content is found in 60% to 80% of all scented hygiene products and cleaning agents like soaps, detergents, shampoos, and body lotions.

Percentage of Linalool Content in 5 Essential Oils

Ravintsara (Cinnamomum camphora) - 50-70%
Rosewood (Dalbergia nigra) - 80–90% (ICUN Red List Endangered Species)
Coriander seed (Coriandrum sativum) - 40-80%
Lavender (Lavandula angustifolia) - 22-45%
Ylang Ylang (Cananga odorata) - 22%

Cineole & Menthol (inhibit 7 fungi)

Cineole - 1,8-cineole (aka eucalyptol) has a fresh mint-like smell and a spicy, cooling taste, It is known for its mucolytic and spasmolytic action on the respiratory system. It has shown therapeutic effectiveness when administered for inflammatory airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD).

Cineole is classified as an oxide - the liberators of aromatherapy. Essential oils having a camphoraceous scent usually contain oxide formations, i.e. eucalyptus and rosemary cineole, among others. The most common oxide in aromatherapy is 1,8-cineole. Also known by a number of synonyms like eucalyptol and cajuputol.

Oxide molecules are chemically very stable and found in many essential oils.

Percentage of Cineole in 5 Essential Oils

Eucalyptus (Eucalyptus globulus & E. radiata) - Up to 90%
Niaouli (Melaleuca quinquenervia) - Up to 80%
Ravintsara (Cinnamomum camphora) - 60%
Rosemary Cineole (Rosmarinus officinalis ct cineolm) - 35-45%
Peppermint (Mentha x piperita) - 18%
Tea Tree (Melaleuca alternifolia) - 5% (Tea Tree’s popular use as one of the most powerful anti fungal oils in aromatherapy is well established. However, according to the research its low percentage of cineole does not bare out its efficacy as an anti-fungal. There are other oils with a much higher cineole content you might want to consider trying). 

Additionally, a study demonstrated that. "Using Tea tree oil cream (10%) appears to reduce the symptomatology of tinea pedis as effectively as tolnaftate (1%) but is no more effective than placebo in achieving a mycological cure." The study concluded, "This may be the basis for the popular use of tea tree oil in the treatment of tinea pedis."

Menthol - has a fresh, minty aroma and is naturally found in mint plants, such as peppermint and spearmint. Menthol is a counterirritant. It promotes relief for minor skin irritations and body aches and pains by giving a cooling then warming sensation. It is frequently added as a flavoring to products like cough drops, beverages, gum and candy.

Menthol is another aroma classified as a monoterpenol.

Percentage of Menthol in 3 Essential Oils

Peppermint (Mentha x piperita) - 29-48%
Spearmint (Menha xo spicata) - less than 1%
Eucalyptus (Eucalyptus radiata) - 2-3%

Anti-fungal Essential Oil Recipe

To a 5ml (100 drops) euro-dropper bottle add:

Palma rosa (Cymbopogon martinii) - 40 drops
Lemongrass (Cymbopogon flexuosus) - 40 drops
Lavender (Lavandula angustifolia) - 10 drops
Eucalyptus (Eucalyptus globulus) - 5 drops
Peppermint (Mentha x piperita) - 5 drops

Cap bottle tightly and shake vigorously to blend oils thoroughly together. Allow blend to synergize for 12 hours or longer before using.

Though the study did not indicate that tinea pedis was one of the fungi tested it may be worth a try to use this EO recipe as a foot fungus treatment.

DIRECTIONS FOR TREATING TINEA PEDIS: Use 12-16 drops diluted in 1tsp of liquid unscented Castile bath soap, or other natural liquid bath soap (acts as a dispersant). Add scented liquid soap to a footpath filled with warm water. Soak foot/feet for 10-15 minutes once or more daily for up to three weeks, or until fungal infection is gone. You can also use the anti-fungal blend suitably diluted in a carrier oil and use as a leave on treatment between foot baths.

READ Related Blogs in this series of articles, 10 Essential Oils with Dominant Antiviral Activity.