Garlic oil is a concentrated liquid extracted from garlic cloves, rich in sulfur-containing compounds that give garlic its sharp smell and most of its biological activity. It comes in several forms, from steam-distilled essential oil used in supplements to simple homemade infusions of garlic in cooking oil. The type you’re dealing with matters quite a bit, because the active compounds, uses, and safety considerations differ depending on how it’s made.
How Garlic Oil Is Made
There are two main types of garlic oil, and they’re surprisingly different products.
Steam-distilled garlic oil is a true essential oil. Garlic cloves are heated with steam, and the volatile compounds evaporate and get collected. This produces a potent, highly concentrated oil that’s mostly sulfur compounds. It’s the type found in capsule supplements and used in research. A chemical analysis of steam-distilled garlic oil identified nine major compounds, with diallyl trisulfide (about 40%) and diallyl disulfide (about 33%) making up nearly three-quarters of the oil. These two compounds are responsible for much of garlic’s antimicrobial and cardiovascular activity.
Garlic oil macerate is what most home cooks and many supplement makers produce. Crushed garlic sits in a carrier oil (often sesame or sunflower) for about a week, allowing the fat-soluble compounds to dissolve into the oil. The process starts by crushing fresh garlic and letting it sit exposed to air for 10 to 15 minutes. That brief exposure triggers an enzyme reaction that converts a stable compound in the raw clove into allicin, the pungent molecule you smell when you chop garlic. The crushed garlic then soaks in oil for seven to eight days. Macerated garlic oil preserves certain fragile compounds, particularly ajoene, that break down during steam distillation. Ajoene stays stable for long periods only in this oil-macerated form.
What’s Actually in It
The signature ingredients in garlic oil are organosulfur compounds, a family of molecules built around sulfur atoms. In steam-distilled oil, the full breakdown looks like this:
- Diallyl trisulfide: 39.8%, the most abundant compound and a major contributor to garlic’s antifungal properties
- Diallyl disulfide: 32.9%, linked to cardiovascular and anti-inflammatory effects
- Diallyl tetrasulfide: 7.1%
- Diallyl sulfide: 7.0%
Together, these four sulfur compounds account for about 87% of the oil. The remaining fraction includes small amounts of other volatile molecules. This composition explains why garlic oil smells intensely sulfurous and why even small amounts pack biological punch.
Blood Pressure and Cholesterol Effects
The cardiovascular benefits of garlic supplements are the most studied area, and the evidence is reasonably strong for people with high blood pressure. A meta-analysis of 12 trials involving 553 people with hypertension found that garlic supplements lowered systolic blood pressure (the top number) by an average of 8.3 mmHg and diastolic pressure (the bottom number) by 5.5 mmHg. A separate dose-response trial found that taking garlic extract daily achieved a 10 mmHg systolic drop within two to three months. For context, that’s a meaningful reduction, comparable to what some first-line blood pressure medications deliver in mild cases.
Cholesterol effects are more modest. A meta-analysis found statistically significant reductions in both total cholesterol and LDL (“bad”) cholesterol in people taking garlic, with earlier research estimating a roughly 10% reduction in total cholesterol. That’s noticeable but unlikely to replace medication for someone with seriously elevated levels. The effects appear strongest in people who already have high cholesterol rather than those with normal readings.
Skin Safety and Topical Use
Garlic oil shows up in folk remedies for everything from ear infections to wound care, but applying it to skin carries real risks. The same sulfur compounds that make garlic biologically active can cause chemical burns and severe irritant contact dermatitis. Allicin, the compound produced when garlic is crushed, can destroy the outer layer of skin cells, breaking down the skin barrier.
Chemical burns from garlic applied to the skin are common enough that medical journals have documented them as a recurring pattern. Crushed raw garlic held against the skin for tooth pain can cause oral chemical burns. Garlic paste applied to wounds or used for tattoo removal has caused second-degree burns. The severity depends on several factors: how the garlic is prepared (raw paste is more dangerous than diluted oil), how long it stays on the skin, whether it’s covered with a bandage (which traps the compounds against the skin), and individual sensitivity. People with existing skin conditions like eczema are at higher risk.
If you’re considering garlic oil for any topical use, dilution matters enormously. Pure garlic essential oil should never go directly on skin. Even diluted preparations warrant caution, and prolonged contact with the skin should be avoided.
Interactions With Blood Thinners
Garlic has a reputation for thinning the blood, which raises questions about combining it with anticoagulant medications. The concern is plausible based on garlic’s known effects on platelet function, and there are isolated case reports of bleeding complications linked to heavy garlic consumption. However, a review published in the British Journal of General Practice found no clear evidence that garlic, whether taken as a supplement or used generously in cooking, causes more frequent bleeding complications or disrupts anticoagulant control in a measurable way.
The mechanism isn’t fully understood. It’s unclear whether garlic’s potential blood-thinning effect comes from reduced platelet function, changes in clotting time, or some combination. The practical takeaway: cooking with garlic is unlikely to cause problems, but if you’re taking blood thinners and considering high-dose garlic oil supplements, it’s worth discussing with whoever manages your medication.
Botulism Risk With Homemade Garlic Oil
This is the safety issue most people don’t know about. Homemade garlic-in-oil mixtures stored at room temperature can harbor the bacteria that produce botulinum toxin, one of the most dangerous foodborne toxins. Garlic is a low-acid food, and submerging it in oil creates an oxygen-free environment, which is exactly what these bacteria need to thrive. Research from the National Center for Home Food Preservation confirmed that garlic-in-oil stored at room temperature poses a real botulism risk.
The rules are straightforward: homemade garlic oil should be refrigerated at 40°F or below and used within four days. For longer storage, freeze it for up to several months. Commercial garlic oil products are safe at room temperature because manufacturers add acid or other preservatives that prevent bacterial growth. If you make garlic oil at home, treat it like a perishable food, not a pantry staple.