Garlic has been used for centuries as both food and medicine.

In fact, eating garlic may provide a wide variety of health benefits (1).

This includes reduced heart disease risk, improved cognitive health, enhanced immune function, and decreased risk of certain types of cancer (2, 3, 4, 5).

This article explains how garlic is particularly protective against the common cold and the flu.

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Mikaela Hamilton/Stocksy United

Garlic can boost immune function

Garlic contains compounds that help the immune system fight germs (4, 6, 7).

Whole garlic contains a compound called alliin. When garlic is crushed or chewed, this compound turns into allicin (with a c), the main active ingredient in garlic (8, 9).

Allicin contains sulfur, which gives garlic its distinctive smell and taste (8, 10).

However, allicin is unstable, so it quickly converts to other sulfur-containing compounds thought to give garlic its medicinal properties (4).

These compounds have been shown to boost the disease-fighting response of some types of white blood cells in the body when they encounter viruses, such as the viruses that cause the common cold or flu (4, 6).


Garlic can be crushed, chewed, or sliced to produce allicin, which is thought to give garlic its immune-boosting properties.

Can garlic help prevent colds and the flu?

Garlic has shown promise as a treatment for preventing colds and the flu.

Studies have shown that garlic may reduce the risk of becoming sick in the first place, as well as how long you stay sick. It may also reduce the severity of symptoms (7, 11, 12).

One study gave 146 healthy volunteers either garlic supplements or a placebo for 3 months. The garlic group had a 63% lower risk of getting a cold. However, there was no significant difference between groups in the time it took to recover from a cold (11).

Another study found that colds were significantly shorter for subjects who ate 2.56 grams of aged garlic extract per day during cold and flu season, compared with a placebo group. Their colds were also less severe (6).

If you often get sick with a cold or flu, eating garlic may help reduce your symptoms or prevent your illness entirely.

However, a review of the evidence found that many of the studies investigating the effects of garlic on the common cold were of poor quality (11).

It’s also unknown if you need to take garlic constantly, or if it also works as a short-term treatment when you start getting sick.


Regularly eating garlic may help prevent the common cold or the flu. If you do get sick, eating garlic may reduce the severity of your symptoms and help you recover faster.

How to maximize the benefits of garlic

The way garlic is processed or prepared can change its health benefits.

The enzyme alliinase, which converts alliin into the beneficial allicin, only works under certain conditions. It can also be deactivated by heat.

One older study found that as little as 60 seconds of microwaving or 45 minutes in the oven can deactivate alliinase, and another study found similar results (13, 14).

However, it was noted that crushing garlic and allowing it to stand for 10 minutes before cooking can help prevent the loss of its medicinal properties.

The researchers also stated that the loss of health benefits due to cooking could be compensated for by increasing the amount of garlic used.

Here are a few ways to maximize the health benefits of garlic:

  • Crush or slice all your garlic before you eat it. This increases the allicin content.
  • Before you cook with your crushed garlic, let it stand for 10 minutes.
  • Use a lot of garlic — more than one clove per meal, if you can.

Ensure whole garlic is crushed, chewed, or sliced before it’s eaten. Let crushed garlic stand for 10 minutes before you cook it.

Garlic supplements

Another easy way to increase your garlic intake is by taking a supplement.

However, be cautious, as there are no regulated standards for garlic supplements.

That means the allicin content and quality can vary, and so can the potential health benefits.

Powdered garlic

Powdered garlic is made from fresh garlic that has been sliced and dried. It doesn’t contain allicin, but is said to have allicin potential.

Powdered garlic is processed at low temperatures and then put inside capsules to protect it from stomach acid.

This helps the enzyme alliinase survive the harsh environment of the stomach so that it can convert alliin to the beneficial allicin in the intestine.

Unfortunately, it’s unclear how much allicin can be derived from powdered garlic supplements. This varies greatly depending on the brand and preparation (15).

Aged garlic extract

When raw garlic has been sliced and stored in 15–20% ethanol for over 1.5 years, it becomes aged garlic extract.

This type of supplement doesn’t contain allicin, but it does retain the medical properties of garlic. Many of the studies showing benefits against colds and the flu used aged garlic extract (2, 6, 16).

Garlic oil

Garlic oil is also an effective supplement, and is typically prepared using steam distillation. It’s typically taken in capsules.

Garlic oil is distinct from garlic-flavored oil used for cooking, which is made by infusing raw garlic into cooking oils.

Homemade garlic oil has also been linked with several cases of botulism, so if you’re going to make your own, make sure to use proper preservation methods (17).


Common types of garlic supplements include powdered garlic, aged garlic extract, and garlic oil. Aged garlic extract may offer the greatest health benefits.

How much garlic should you eat per day?

While there is no established effective dosage of garlic, some studies on raw garlic use 100 mg crushed raw garlic per kilogram of body weight twice per day. This equals about three to four cloves per day (18).

You may also take an aged garlic extract supplement. Studies investigating the health benefits of aged garlic use varying dosages ranging from 240 mg to 2,560 mg (6, 19).

High intakes of garlic supplements can be toxic, so don’t exceed the dosage recommendations.


There is no established effective dosage of raw garlic or garlic supplements. Since high intakes of garlic supplements can be toxic, don’t exceed the dosage recommendations.

Other tips to boost immune function

Here are five more ways to boost immune function and help you avoid colds and the flu:

  1. Consider a probiotic. Probiotics may promote a healthy gut, enhance immune response, and reduce risk of infection in some people (20, 21, 22, 23, 24).
  2. Eat a balanced diet. Your whole diet is important. Getting a balance of important nutrients will help ensure your immune system stays in good shape.
  3. Don’t smoke. Cigarette smoke can weaken the immune system and make you more prone to infection (25, 26).
  4. Avoid excess alcohol. Excess alcohol is thought to damage the immune system and make you more susceptible to infection (27, 28).
  5. Take a zinc supplement. Take zinc lozenges or syrup within 24 hours of the start of a cold, as this may reduce the duration of the cold (29).

Eating a balanced diet and maintaining a healthy lifestyle are essential for keeping your immune system in good shape.

The bottom line

Studies suggest that garlic may help fight colds and the flu. It may reduce your risk of developing an illness, and help you recover faster.

To maximize these benefits, it’s best to consume raw garlic or aged garlic extract.

At the end of the day, garlic is both tasty and super nutritious. There are many excellent reasons to include it in your diet.