The Chemical Causes for the Smell in Garlic

November 29, 2025 •

3 min read

An estimated 150 million pounds of garlic are consumed annually in the United States, and its pungent aroma is central to its appeal. However, a raw, intact garlic clove has very little scent; its characteristic odor only appears when it is crushed or chopped. This distinctive smell is primarily caused by a chemical compound called allicin, which is created through a fascinating enzymatic reaction.

Quick Summary

The unmistakable odor of crushed garlic is caused by the sulfur compound allicin, which forms when the enzyme alliinase reacts with the odorless compound alliin after the clove is damaged. This unstable allicin further breaks down into other volatile sulfur compounds that contribute to garlic's pungent aroma and linger on the breath and skin.

Key Points

Allicin is the main cause: The powerful and pungent smell of freshly crushed garlic is primarily due to the compound allicin, an organosulfur compound.
Enzymatic reaction is the trigger: Allicin is not present in whole cloves; it is formed when the enzyme alliinase reacts with the amino acid alliin after the garlic is damaged.
Unstable compound: Allicin is unstable and quickly breaks down into a number of other volatile sulfur compounds, which contribute to the lingering and persistent garlic smell.
Lingering odor culprit: One key breakdown product, allyl methyl sulfide (AMS), is absorbed into the bloodstream and excreted slowly through the breath and pores, causing lasting body odor.
Cooking affects odor: The way garlic is prepared influences its smell; mincing produces the strongest odor, while heating or cooking can deactivate the enzyme and reduce the odor's intensity.

The Alliin-Allicinase Reaction: How the Smell is Born

When a garlic clove is whole and undamaged, it contains two important compounds stored in separate compartments within its cells: the odorless amino acid alliin and the enzyme alliinase. This separation prevents any chemical reaction from occurring. However, when garlic is crushed, chopped, or bruised, the cell walls are broken, allowing the alliin and alliinase to mix.

The enzyme alliinase acts rapidly upon the alliin, catalyzing a reaction that produces a new, volatile, organosulfur compound: allicin. This reaction is incredibly fast, and the allicin is the major initial contributor to the familiar, pungent scent of fresh garlic. Allicin's creation is a defense mechanism developed by the garlic plant to ward off pests and pathogens.

The Breakdown: From Allicin to Lingering Odor

Allicin is highly unstable and quickly begins to decompose into a cascade of other sulfur-containing compounds. This breakdown explains why the aroma of crushed garlic evolves over time. These secondary compounds are also volatile and contribute to garlic's lingering smell, often referred to as "garlic breath" and body odor. A prominent compound formed from this decomposition is allyl methyl sulfide (AMS).

The Volatile Culprits

Several volatile organic sulfur compounds (VOSCs) are responsible for the complex and persistent scent of garlic. These include:

Diallyl disulfide
Allyl methyl sulfide (AMS)
Diallyl trisulfide
Allyl mercaptan

Of these, allyl methyl sulfide (AMS) is particularly noteworthy. Unlike the other compounds, AMS is not easily metabolized by the body. It is absorbed into the bloodstream from the gastrointestinal tract and then slowly released through the lungs (causing bad breath) and skin pores (causing body odor). This process can take up to a day or more, which is why the effects of consuming garlic can be so long-lasting.

Comparison of Key Garlic Compounds

To better understand the different chemical players, consider this comparison:


Feature	Alliin	Allicin	Allyl Methyl Sulfide (AMS)
Scent	Odorless	Major, pungent component of fresh-crushed garlic	Lingering "garlic breath" and body odor
Location in Clove	In the cytoplasm of cells	Only formed when cloves are damaged	Produced as a breakdown product inside the body
Stability	Stable	Unstable, short half-life	Stable, slowly excreted by the body
Production Trigger	Stored in intact cloves	Enzyme alliinase reacts with alliin upon crushing	Metabolism of allicin after consumption

Controlling the Smell in Cooking and Beyond

The way garlic is handled directly impacts the amount and type of odorous compounds produced. Mincing or crushing garlic maximizes the cell damage, leading to the highest concentration of allicin and, subsequently, its potent breakdown products. Conversely, cooking garlic cloves whole or lightly sautéing them can result in a milder flavor and less odor, as heat can deactivate the alliinase enzyme and prevent the full conversion to allicin.

For those who want to mitigate the lingering effects of garlic on breath and body odor, certain remedies have been suggested, including consuming milk, parsley, or apples. The effectiveness of these methods varies, but they primarily work by masking the odor or through chemical reactions that neutralize the sulfur compounds. Some research even suggests that rubbing your hands on stainless steel can help remove the odor after handling raw garlic, as the sulfur compounds may bond with the metal.

Conclusion

While many people credit a single, mysterious "garlic chemical" for its famous aroma, the truth is a fascinating story of chemical transformation. The iconic smell is the result of a precise and rapid enzymatic reaction, triggered by the simple act of crushing the clove. This process creates allicin, which then gives rise to a family of volatile sulfur compounds, each contributing to the powerful and persistent character that defines garlic's unique place in our kitchens and on our palates. For a deeper dive into the science, a review on allicin's chemistry and biological properties provides excellent authoritative information.

Frequently Asked Questions

The primary chemical that creates the smell of fresh, crushed garlic is allicin, an organosulfur compound formed through an enzymatic reaction.

No, an intact, whole garlic clove has very little odor. The distinctive smell is only released when the clove is crushed or chopped, which activates the enzyme that creates allicin.

Alliin is an odorless sulfur compound stored within garlic cells, and alliinase is an enzyme stored in a separate compartment. When the clove is damaged, they mix and react to form allicin.

Garlic breath can last a long time because the body metabolizes allicin into other volatile sulfur compounds, such as allyl methyl sulfide (AMS), which are then slowly released through the breath and pores over many hours.

Yes, cooking can change the smell of garlic. High heat can deactivate the alliinase enzyme, preventing allicin from forming and resulting in a milder, less pungent flavor and aroma.

Yes, allicin is unstable and breaks down into a cascade of other volatile sulfur compounds like diallyl disulfide and allyl mercaptan, all of which contribute to the complex aroma.

Allicin is associated with many potential health benefits, including antimicrobial, antioxidant, and immunomodulatory properties, though its instability can make its therapeutic use challenging.