Fatty Acids

Adults have an acidic, fatty substance in and on the skin called sebum. Sebum functions as a natural antifungal agent, part of the innate immune system. Fatty acids have been used for years with the idea that if a substance similar to sebum could be applied to the infected area, the effect of the sebum would be augmented and fungi could be eradicated. The application of fatty acids or their salts does in fact have an antifungal effect, albeit a feeble one.

The higher-molecular-weight fatty acids have the advantage of having lower volatility. Salts of fatty acids are also fungicidal and provide nonvolatile forms for topical application.

Propionic Acid

Propionic acid is an antifungal agent that is nonirritating and nontoxic. After application, it is present in perspiration in low concentration (—0.01%). Salt forms with sodium, potassium, calcium, and ammonium are also fungicidal. Propionic acid is a clear, corrosive liquid with a characteristic odor. It is soluble in water and alcohol. The salts are usually used because they are nonvolatile and odorless.

Zinc Propionate

Zinc propionate occurs as an anhydrous form and as a monohydrate. It is very soluble in water but only sparingly soluble in alcohol. The salt is unstable to moisture, forming zinc hydroxide and propionic acid. Zinc propionate is used as a fungicide, particularly on adhesive tape.

Sodium Caprylate

Sodium caprylate is prepared from caprylic acid, which is a component of coconut and palm oils. The salt precipitates as cream-colored granules that are soluble in water and sparingly soluble in alcohol.

Sodium caprylate is used topically to treat superficial dermatomycoses caused by C. albicans and Trichophyton, Microsporum, and Epidermophyton spp. The sodium salt can be purchased in solution, powder, and ointment forms.

Zinc Caprylate

Zinc caprylate is a fine white powder that is insoluble in water or alcohol. The compound is used as a topical fungicide. The salt is highly unstable to moisture.

Undecylenic Acid

10-Undecenoic acid (Desenex, Cruex) obtained from the destructive distillation of castor oil. Undecylenic acid is a viscous yellow liquid. It is almost completely insoluble in water but is soluble in alcohol and most organic solvents.

Undecylenic acid is one of the better fatty acids for use as a fungicide, although cure rates are low. It can be used in concentrations up to 10% in solutions, ointments, powders, and emulsions for topical administration. The preparation should never be applied to mucous membranes because it is a severe irritant. Undecylenic acid has been one of the agents traditionally used for athlete's foot (tinea pedis). Cure rates are low, however.


Glyceryl triacetate (Enzactin, Fungacetin) is a colorless, oily liquid with a slight odor and a bitter taste. The compound is soluble in water and miscible with alcohol and most organic solvents.

The activity of triacetin is a result of the acetic acid released by hydrolysis of the compound by esterases present in the skin. Acid release is a self-limiting process because the esterases are inhibited below pH 4.

Salicylic Acid and Resorcinol

Salicylic acid is a strong aromatic acid (pKa 2.5) with both antiseptic and keratolytic properties. It occurs as white, needlelike crystals or a fluffy crystalline powder, depending on how the compound was brought out of solution. Salicylic acid is only slightly soluble in water but is soluble in most organic solvents. The greater acidity of salicylic acid and its lower solubility in water compared with p-hydroxybenzoic acid are the consequence of intramolecular hydrogen bonding.

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