Caprylic acid is a medium-chain fatty acid with eight carbon atoms, found naturally in coconut oil, palm kernel oil, and the milk of several mammals. It has gained attention for its antimicrobial properties, its role in ketone production, and its potential cognitive benefits. Most people encounter it either as a component of MCT oil supplements or as an ingredient in skincare products.
Chemical Basics and Natural Sources
Caprylic acid (also called octanoic acid) has the molecular formula C8H16O2. It’s a saturated fatty acid, meaning its carbon chain has no double bonds, which makes it chemically stable. The “medium-chain” label refers to its length: with eight carbons, it falls between the short-chain fatty acids produced by gut bacteria and the long-chain fatty acids that make up most dietary fats.
Coconut oil is the richest common food source, with caprylic acid making up 6 to 10% of its total fatty acids. Palm kernel oil contains 2 to 5%. Among animal sources, goat milk has about 3% caprylic acid, cow milk 1 to 2%, and human breast milk roughly 0.5%. Rabbit milk is unusually rich in it, reaching 15 to 18%. When you buy an MCT oil supplement, caprylic acid is typically the primary or sole fatty acid included, because it has the strongest metabolic effects of the medium-chain group.
How Your Body Processes It
What makes caprylic acid metabolically interesting is its size. Fatty acids with eight or fewer carbons can cross directly into the energy-producing compartments of your cells (the mitochondria) without needing the transport system that longer fatty acids require. This shortcut means caprylic acid gets converted to energy, and specifically to ketones, much faster than other fats.
The ketone-producing effect of caprylic acid is roughly three times stronger than that of capric acid (a 10-carbon chain) and six times stronger than lauric acid (12 carbons). In one study, plasma ketone levels rose for about four hours after consuming caprylic acid, while capric acid produced no measurable increase at all. This is why caprylic acid is the preferred ingredient in MCT oils marketed for ketogenic diets or cognitive energy: gram for gram, it generates more ketones than any other dietary fat.
Antifungal and Antibacterial Effects
Caprylic acid’s antimicrobial activity is one of the main reasons people seek it out as a supplement. Its primary mechanism is physical: the molecule is small enough to penetrate and disrupt the cell membranes of fungi and bacteria. Molecular simulations show that caprylic acid readily inserts itself into lipid membranes and destabilizes their structure, while longer fatty acids like lauric acid tend to clump together and barely interact with the membrane at all.
Against Candida albicans, a common yeast responsible for oral thrush, vaginal yeast infections, and intestinal overgrowth, caprylic acid causes rapid, dose-dependent changes in membrane integrity. Lab tests showed a 20% change in membrane stability within 10 minutes of exposure, peaking at about 32% after 30 minutes. Beyond direct killing, caprylic acid also inhibits processes that make Candida harder to treat: it interferes with the yeast’s ability to change shape, stick to surfaces, and form the protective biofilms that shield colonies from the immune system.
On the bacterial side, caprylic acid is effective against several common pathogens. Testing against five species, including Staphylococcus aureus, multiple Streptococcus species, and E. coli, caprylic acid reduced all five by more than 100,000-fold within six hours. Streptococcus species were most sensitive, while E. coli showed the most tolerance.
Cognitive Health and Alzheimer’s Research
The brain normally runs on glucose, but it can also use ketones as fuel. In Alzheimer’s disease, the brain’s ability to use glucose declines, which has led researchers to investigate whether boosting ketone availability through caprylic acid supplementation could help compensate.
Three randomized, placebo-controlled trials in patients with mild cognitive impairment or mild-to-moderate Alzheimer’s found that supplementation with MCT oil rich in caprylic acid significantly improved cognitive scores. A separate review of eight patients with mild-to-moderate Alzheimer’s who took 20 grams per day of a caprylic acid preparation for six months or longer showed delayed cognitive decline compared to patients on standard drug therapy alone.
A larger observational study tracking participants over 13 years found a more nuanced picture. Higher circulating levels of caprylic acid were associated with a reduced risk of developing mild cognitive impairment among cognitively normal women, people with at least one cardiometabolic condition, and those carrying a genetic risk factor for Alzheimer’s. However, among people who already had mild cognitive impairment, higher caprylic acid levels did not reduce the risk of progressing to full Alzheimer’s disease. The short version: caprylic acid may offer some protective benefit early on, but it does not appear to reverse established disease.
Skin and Acne
Caprylic acid shows up in skincare formulations, particularly those targeting acne. Its antimicrobial properties extend to the bacteria involved in breakouts. In lab testing, a topical blend containing caprylic acid inhibited the growth of the primary acne-causing bacterium at a concentration of just 0.125%, and Staphylococcus aureus at 0.25%.
In a clinical trial, applying this blend for 28 days reduced skin oiliness, lowered levels of porphyrins (a marker of bacterial activity in pores), and decreased the number of inflammatory lesions. Dermatologists evaluating the participants noted improvements in overall skin appearance, acne presence, and lesion size. Part of the effect may come from the blend’s ability to reduce the activity of an enzyme called 5-alpha reductase, which influences oil production in the skin. Expression of this enzyme dropped by 24% compared to controls.
Safety and Side Effects
Caprylic acid consumed through food is considered safe. As a supplement, it is generally well tolerated for short-term use, with the most common side effects being stomach discomfort and changes in taste. There is no established standard dosage for supplemental caprylic acid. Clinical trials have used a range of doses, with cognitive studies typically administering around 20 grams per day of MCT oil composed mostly of caprylic acid.
Because caprylic acid is rapidly absorbed and metabolized by the liver, people with significant liver conditions should approach concentrated supplements cautiously. Starting with a low dose and increasing gradually is a common practical strategy for minimizing the digestive side effects that high-dose MCT oils sometimes cause, particularly nausea, cramping, and loose stools. Taking it with food also helps.