Garlic oil is a concentrated liquid extracted from garlic cloves, rich in sulfur-containing compounds that give garlic its distinctive smell and most of its biological activity. It comes in several forms depending on how it’s made, and each form has a different chemical profile. You’ll find garlic oil sold as a dietary supplement, a cooking ingredient, and an ingredient in topical products.
How Garlic Oil Is Made
There are two main types of garlic oil, and they’re quite different products despite sharing a name.
Steam-distilled garlic oil is the essential oil form. Garlic cloves are heated with steam, and the volatile compounds rise with the vapor and are collected. This process captures sulfur compounds like diallyl disulfide and diallyl trisulfide but destroys allicin, the compound most people associate with fresh garlic’s health effects. Allicin is unstable and breaks down during the heating process.
Oil-macerated garlic is made by crushing raw garlic cloves and soaking them in a carrier oil, typically soybean or olive oil. When garlic is crushed, an enzyme converts a dormant compound called alliin into allicin. That allicin then quickly breaks down into other biologically active compounds, including dithiins, ajoenes, and various sulfides. Macerated garlic oil tends to contain more of these fat-soluble breakdown products than the steam-distilled version.
Beyond these two, you’ll also encounter dehydrated garlic powder (often sold in capsules) and aged garlic extract, which is garlic soaked in alcohol for months. Each of these four garlic products has a meaningfully different chemical makeup.
What’s Actually in It
Steam-distilled garlic oil is dominated by a handful of sulfur compounds. The two most abundant are diallyl disulfide and diallyl trisulfide, which together typically make up 50% to 80% of the oil depending on the garlic’s origin and extraction method. Commercial Chinese garlic oil, for example, contains 45% to 63% diallyl disulfide and 18% to 23% diallyl trisulfide. Greek garlic oil analyzed in lab studies showed a more even distribution, with diallyl disulfide at 23% to 28% and diallyl trisulfide at 18% to 22%.
Smaller but notable amounts of allyl methyl trisulfide (roughly 8% to 18%), allyl methyl disulfide (4% to 12%), and diallyl tetrasulfide (up to about 10%) round out the profile. These sulfur compounds are what make garlic oil smell intensely of garlic, and they’re also responsible for most of its studied biological effects. Diallyl disulfide in particular has been identified as the active compound behind garlic’s effects on cardiovascular markers.
Effects on Blood Pressure and Cholesterol
Garlic supplements have the strongest research support for cardiovascular effects. A meta-analysis of 12 trials involving 553 people with high blood pressure found that garlic supplements lowered systolic blood pressure by an average of 8.3 mmHg and diastolic blood pressure by 5.5 mmHg. Those reductions are comparable to what some standard blood pressure medications achieve.
Cholesterol is the other well-studied area. A larger meta-analysis of 39 trials and 2,300 participants found that garlic supplements improved total cholesterol and LDL (“bad”) cholesterol in adults who had mildly elevated levels to begin with. The benefits were most apparent in people whose cholesterol was already trending high, not in people with normal levels.
It’s worth noting that these meta-analyses included various garlic preparations, not garlic oil exclusively. The active compounds overlap, but the specific form and dose matter.
Antimicrobial and Antifungal Properties
Garlic oil can kill or inhibit the growth of certain bacteria and fungi. Lab research on Candida albicans, the yeast responsible for most fungal infections in humans, showed that garlic oil penetrates the cell membrane and damages internal structures like mitochondria, ultimately killing the cell. It also disrupts how the yeast produces energy and processes proteins.
These findings are from laboratory studies, not clinical trials in people. Garlic oil’s ability to kill microbes in a petri dish is well established, but that doesn’t automatically translate to treating infections in the body. Still, this antimicrobial activity is part of why garlic has been used in traditional medicine for centuries and why it appears in some topical formulations.
Hair and Skin Uses
Garlic has a long history in traditional medicine as a treatment for hair loss, particularly alopecia areata, and it’s now added to some commercial hair care products. Animal research has shown that garlic-derived compounds applied to the skin can stimulate hair follicles to enter their active growth phase by triggering several growth-promoting signaling pathways. In rat studies, topical garlic application increased the number of actively growing hair follicles and boosted follicle diameter without causing visible skin irritation.
There’s a practical tension with topical use, though. Concentrated garlic extracts applied directly to skin can cause allergic contact dermatitis, and in rare cases, the sulfur compounds in garlic oil have caused chemical burns when used under bandages or occlusive dressings. If you’re considering topical garlic oil for hair or skin, dilution in a carrier oil is standard practice.
Typical Supplement Doses
Garlic oil supplements are sold in soft gel capsules, usually containing the steam-distilled essential oil. The commonly suggested daily dose for garlic oil specifically is 2 to 5 mg. For context, that’s a small amount of concentrated oil, roughly equivalent to the volatile compounds you’d get from 2 to 5 grams of fresh raw garlic (about one to two cloves). Other garlic supplement forms use different dose ranges: 300 to 1,000 mg for dried garlic extract, or 2,400 mg per day for aged garlic extract in liquid form.
Blood Thinners and Drug Interactions
Garlic is commonly listed as something to avoid if you take blood-thinning medications like warfarin, because of its theoretical ability to enhance anticoagulant effects. However, the actual clinical evidence for this interaction is thin. A review in the British Journal of General Practice found no evidence that garlic consumption, whether as a supplement or in cooking, was associated with more bleeding complications or worse blood-thinning control. The data that does exist is limited to scattered case reports and anecdotes. That said, if you’re on anticoagulants and want to take concentrated garlic oil supplements (as opposed to just cooking with garlic), it’s reasonable to mention it to your prescriber.
Botulism Risk With Homemade Garlic Oil
This is the most important safety point for anyone making garlic-infused oil at home. Raw garlic can carry spores of Clostridium botulinum, the bacterium that causes botulism. These spores are harmless in the presence of oxygen, but when you submerge garlic in oil, you create an oxygen-free environment where the spores can germinate and produce a dangerous toxin. The oil won’t look or smell off.
If you make garlic oil at home using fresh garlic, refrigerate it and use it within two to four days. The spores don’t grow well at refrigerator temperatures. For infused oils made with dried herbs or garlic, refrigeration extends the safe window to about three months. Commercially produced garlic oils are processed with acidification or other controls that prevent this risk, so shelf-stable products from the store don’t carry the same concern.